Delia is back, with a new TV series and a new book. Calloo callay, hang out more flags, etc. When she said she was retiring four years ago, fellow cooks wrote farewells that were almost like obituaries, but fonder. Even Antony Worrall Thompson wrote 'Why We'll Miss Mummy Delia' though she had publicly described him as 'repulsive'. She told our Nigel Slater that she would never do television again. Well, never say never. Actually she has retired more often than Frank Sinatra but, at a mere 66, I imagine she has many more retirements to come.

Anyway, good. I learned to cook from Delia's Complete Cookery Course when my husband died five years ago and I found that what people told me was right - Delia works. She might be dull, but she is infallible. That doesn't necessarily mean I'll like her though - she always seems so prissy on television. And she is keen on religion and football, two of my pet hates. But I remember John Peel who was a neighbour of hers in Suffolk telling me years ago that she was really good fun, and recently Simon Hopkinson said the same - get her relaxed and she's a laugh a minute. So I hoped this was the Delia I was going to meet.

Alas, not this time. There was a lot of heavy negotiation and control freakery beforehand because she demanded copy approval (no) which I thought before I met her was probably the fault of her PR but now think more likely came from Delia. Also her 'people' sent my 'people' (I love this idea that we all have whole nations of underlings at our command) the menu of the hotel where we were meeting so that we could pre-order our lunch. I spent a lot of time dithering about which menu choices Delia would approve and opted for a beef pie that seemed to say 'I am a plain, unpretentious Delia fan unswayed by foodie fashions'. But on the day, when I was already in the taxi, I received a message that we would have a 'mixed platter' instead. I think if I was the sort of person who had people I would have thrown a hissy fit at this point and turned the taxi homewards, but anyway we had a platter and very nice it was. In fact it was so nice that Delia said she'd send one of her Norwich City football club people (she and her husband are majority shareholders and huge donors to the club) to see it because maybe their Norwich sandwich offerings were getting a bit dull. Why don't you just describe the platter? I suggested, but she said no, she wouldn't remember all the details. It is at moments like this that you realise what it means to be a perfectionist - Delia will send people from Norwich to London to look at a plate of sandwiches.

So anyway, there we were beaming at each other over the sandwich platter in a London hotel suite and telling each other how much we both loved Simon Hopkinson, so in theory all ready to bond. But it never happened. I quickly got irritated by the fact that any time I quoted anything from the cuttings, she said 'Oh no, that's wrong. I never said that'. Of course some journalists do misquote, or make mistakes, but it is impossible for as many journalists to make as many mistakes as Delia claims. She obviously loathes the press - despite the fact that she is married to a journalist and used to be a journalist herself.

Also there is the small problem that I hate her book (I haven't yet seen the television series), starting with the title, How to Cheat at Cooking. How could she? Delia is not someone we want cheating - there are plenty of other telly cheffies doing that - her forte has always been showing you the correct way to do things. Whereas her new book keeps recommending instant potato and - horror of horrors - frozen diced onions. I mean even I can chop an onion in the time it takes to find something in the freezer. At times, I even wondered if her book was intended as a wicked parody of Nigella Express. Assembling the ingredients for one of her recipes would mean shopping for days, and anyway I couldn't find anything I wanted to make. In the end I decided to stick a pin to choose a recipe, but when I landed up with 'West African groundnut stew' and found I needed to buy a jar of jalapeno peppers, a jar of Whole Earth crunchy organic peanut butter, a packet of English Provender Very Lazy ginger, another of Seasoned Pioneers African Tsire powder plus some 'ready-prepared diced mixed carrot and swede' I gave up.

Actually her first ever cookbook (which became a bestseller in 1971) was also called How to Cheat at Cooking, but she says this one is completely different, 'Because cheating has come on a lot! There are so many fantastic ingredients now in supermarkets and specialist shops and farmers' markets and delis, that I just wanted to show what is out there to take some of the preparation out of cooking.' But we don't want you to take the preparation out, we want you to keep it in, I wailed. 'I know, I know. You're right. And people don't like the title but I think I was just emotionally attached to it because it was my first book. And nobody, honestly, could come up with anything better. We all tried.' The idea, she says, is that you stock your freezer and store cupboard (you would need a cupboard as big as a house) and then you can just whiz home and rustle up your West African groundnut stew or whatever. 'I've never said this is how to cook. I've said this is how to cook when you're busy.' But telling us to buy diced onions ...? 'I didn't say buy them; I said they are available. And a lot of people don't want to chop onions because it makes their mascara run.' Oh really.

The book is very specific about what you need in your store cupboard and names certain products over and over again, so presumably there will be the same 'Delia Effect' that meant stores ran out of cranberries when she recommended them in 1995, and a firm that made omelette pans had to up its production from 200 a year to 90,000 in four months. This time it will be the Kenwood mini chopper, the Braun 300W stick blender and a product called Aunt Bessie's Homestyle instant mashed potato that she seems to recommend on almost every page. Delia sharply corrected me and said it only occurred in 'about three' recipes but I checked afterwards and found it in seven, including one for chocolate cupcakes.

If any other cookery writer did this, one might wonder if they had some tie-up with Aunt Bessie's. But not Delia. 'I mean we had huge offers for me to do advertising but I've never done it. I don't think I'd still be sitting here publishing a cookery book if I'd gone down that route. Which leaves me blissfully free. So when I say the best product is this, people trust me.' Does she disapprove of people like Jamie Oliver who do do advertising? 'No. I don't disapprove at all, and I think he's done an awful lot of good with Sainsbury's. It's just something that I personally wouldn't be able to do. Unless, Lynn,' she giggles, 'I was never ever going to do any more recipes. And then - I'm not sure - but if we needed a striker in the football club .... No, that's a bit tongue in cheek - I don't think I really would.'

I said maybe she ought to warn manufacturers beforehand that they're about to see the Delia Effect and she said soberly, 'We always do. I always have done all my career - though most people have ignored me. It's not me, it's the power of television.' She says that one of the ingredients she recommends in this book, Dress Italian tomato sauce ('It smells like an Italian kitchen - absolutely beautiful') is currently only available in Waitrose and her people have been phoning other supermarkets telling them to stock it. 'We want to get everybody geared up, because the book could fall absolutely flat if the ingredients are not available.'

Hmm. I've lent the book to several keen cook friends and none of them has come back raving. But maybe the television series will make it a hit. She says she didn't intend to put it on television originally, 'It was just going to be a book, and I started working on the recipes. But one day I was sitting writing a recipe and I just thought, This would be much clearer if it was on TV. It's very hard to teach people completely from the written word - I always remember it took 800 words to teach people how to make an omelette and about one minute to show them.'

But she wanted this television series to be different. All her previous series were made in the conservatory-kitchen that she had specially built at her home, but it still felt like a studio and she wanted to get out. (Perhaps she was remembering the great cat tragedy of 1999 when she forbade the television crew filming How to Cook from using her loo. They ordered a Portaloo and watched it being lowered from the lorry onto one of her cats.) Anyway, this time she wanted to make a less kitchen-bound programme so the BBC sent her to Documentaries in Bristol who said 'Well fine, but we need to see a bit of your life as well because we're documentary makers, we can't just do cookery'. So the series includes snippets of her life - Delia going shopping, going to Mass, going to a football match with her husband, visiting friends (including Sister Wendy Beckett and another nun), eating in restaurants. Wasn't she nervous about all this camera intrusion? 'No. Because if I didn't want them to film something I just said no.'

Oh, of course. For a moment I'd forgotten the famous Delia iron will that makes Mrs Thatcher seem like a soft touch. My Delia moment came when I mentioned the name of her first boyfriend, who was important because he introduced her to Catholicism and also unintentionally set her on the path to cooking by telling her that his previous girlfriend was a wonderful cook. 'Oh Lynn, please please please!' she said, opening her eyes very wide, 'Can I ask you the most enormous favour? That you won't mention his name. If you could just say "a boyfriend" I would be so grateful.' And lo, somehow against all my principles, I found myself promising not to mention his name, though you can find it by reading the Delia articles on Google. Not a famous name anyway.

Was she always like this, or was she more malleable when she started? 'No. Not at all. I remember once when I was having a big fight with someone, it might have been over a book cover, I said to Debbie [Owen, her agent and friend] "Do you think I'm difficult? Do you think because I've had a lot of success, it's made me more difficult?" And she said, "No, you were like it from day one!".' But that's pretty extraordinary, given that she first met Deborah Owen almost 40 years ago, when she was a complete nobody.

How did it happen? Whence cometh the phenomenon that is Delia? She doesn't make it easy to find out - getting biographical facts out of her is like hewing coal. Her Who's Who entry lists all her books but not her date of birth or education. One cutting I read said that her father was an RAF radio operator - in fact she told me he had his own printing-finishing company making display material. Another cutting said her parents split up after 46 years of marriage - ridiculous, she says, they split up when she was 15 or 16.

All we can establish is that she was born in Woking in 1941, and grew up in Bexleyheath, with a younger brother. She failed her 11-plus and went to Bexleyheath Secondary Modern School which she left at 16 without a single O-level. She never says she is dyslexic but she told me she can't spell and 'Sometimes I come to a word and I just haven't got a clue'. So she writes everything longhand and her husband types it onto the computer. When she signed her cookbook for me, she asked, How do you spell Lynn? And I said 'L.Y.N.N. without an E' and she wrote Lynne. So perhaps that's the reason why she did badly at school. She eventually became a washer-up and then waitress at a restaurant called The Singing Chef that featured different French regional cuisines every week. The chef was so pleased with her enthusiasm he gave her three books - Elizabeth David's French Provincial Cooking, The Penguin Book of Wine and The Grammar of Cookery by Philip Harben, which she found very good on basics. Then one day a customer told her that English cooking used to be the best in the world so she took herself to the reading room of the British Museum - which must have been daunting for a girl with no O-levels - and read her way through old English cookbooks till she discovered her heroine, Eliza Acton. She says that Mrs Acton is much better than Mrs Beeton because she obviously tested her recipes thoroughly.

Then she saw an advertisement for a cookery writer at the Mirror magazine, got the job and met Michael Wynn-Jones, the deputy editor, whom she married in 1971. The magazine folded almost immediately but she went on to write for other papers - the Evening Standard for many years - while he formed his own publishing company. Her first cookbook, How to Cheat at Cooking, was a bestseller, and the rest is more or less history. She and her husband still live in the same Suffolk cottage they bought for £4,000 when they first married - it is a bit small, she concedes, but they've added or converted bits over the years and they love it. Sadly, they were never able to have children but she has a niece and nephew, and of course the 'great community' of Norwich City Football Club. Her husband has now retired though he still runs the deliaonline website, and does all her typing. Nowadays he does most of the cooking, too. They never give dinner parties (or go to them) because they make her nervous and anyway, they can only seat eight round their dining table and only do that at Christmas.

When she does cook, she follows her own recipes but they still sometimes go wrong. 'Oh yes,' she says earnestly, 'it does happen. Sometimes now, being older, I can have missed out a whole ingredient or not read the recipe properly. I once made a cheesecake for someone coming to supper that night and I got to the end and it said - in my own recipe - "Now cover it with clingfilm and leave it in the fridge overnight".'

Just the other day, she says, her marmalade caught on the pan because she had a new hob and the temperature was too high, and now it's got all these black flecks in it. It doesn't really matter, she says unconvincingly, because it tastes just as good, but I bet she freaks out every time she sees those black specks.

She is a perfectionist who goes berserk when anything is wrong. The only thing that soothes her is going to Mass. She was taken to Mass for the first time in her twenties by the unnamed boyfriend (who went on to become a priest) and eventually took instruction and converted. She was always interested in religion, she says, and loved scripture lessons at school because she was always asked to read the Bible - 'That was the only thing they picked me for. But I always thought Catholics were people who had loads of children so they'd get more Catholics, you know - that was my narrow view. Then I went to Mass and it was all in Latin and I didn't understand a word of it, but I thought, Whatever's going on up there is authentic. That is real. So then I started to have instruction and I loved it.'

Since then she has gone to Mass every day of her life, almost without fail. When she and her husband go on driving holidays abroad, which they love doing, he makes it his job to look up all the places and times of Mass on the internet - the only country he ever failed in was Morocco. He drives her to Mass and then waits in the bar - she has never even tried to convert him, possibly because his father was an Anglican vicar and he was 'brought up with a lot of church', but also because she believes, in some mysterious way, that atheists are closer to God than many religious people.

Debbie Owen once said that Delia's faith was 'a vital safety valve ... She gets very annoyed about things sometimes and it helps soothe her ... I think she would admit herself that she would be unbearable to live and work with without her faith.' Delia agrees, and adds, 'If I didn't go to Mass every day, I might be 10 times worse. A journalist once wrote about me, "She goes to Mass every day but then she comes back and makes her secretaries cry". And it's true!' She roars with merry laughter while I just gawp at her. Why does she make her secretaries cry? 'The thing is I'm a perfectionist, and I have made people cry. But the point I'm trying to make is that being as enthusiastic as I am about my faith does not make you a good person. It doesn't! What it does is it makes you relaxed and happy in your weakness and knowing that I love God but I'm not God.'

She has said that she dislikes her prim image on the telly, and that 'Everybody who knows me says I can't believe you're so different on telly, you're just not the same person'. She thinks it derives from the fact that she's concentrating so hard and also that she decided from the outset that she wanted the food to be the star. But she says her one regret about her career is that she listened too much to producers who, if she made a mistake, made her do it again. 'If I took a ladle full of jam out of the pot and it dripped a bit, they'd say Stop, clean up, do it again. So it all comes across as so perfect because they're making me do it perfect. And that's not how it should be!'

Quite - and the public is always thrilled on those rare occasions when her perfection slips, as for instance when she called Antony Worrall Thompson 'repulsive' - though predictably she says, 'I was misquoted quite extensively on that'; or the other famous occasion three years ago when she reeled onto the pitch at half time in a Norwich City match against Manchester City and started yelling 'Let's be having you!' at supporters. Everyone assumed she was drunk but, she insists, 'I wasn't actually. I had had some wine with my supper. But actually I had heels on and it was muddy so it was quite difficult to walk so I did look a bit sort of odd. I wanted to tell the fans to start cheering because the week before we had been losing and the fans got behind the team in such a vocal way that we actually scored three goals in about four minutes. But I made an enormous mistake, which was that I forgot Sky TV was there.'

But was it such an enormous mistake? After all, the public was delighted. 'The press were pretty awful for the first two days. One of them said I should be reported to the FA - it was all terrible! And then all of a sudden the whole thing changed and suddenly now it's wonderful. Whenever I go to an away match all the other supporters say. "Hi Delia! Let's be having you!" It's really nice.' So isn't the moral that she can afford to let herself go a bit, be less than perfect, without losing public affection? 'Maybe yes,' she says doubtfully. 'Let's see what happens now, with this new series. If people want it, fine. If they don't want it, it doesn't matter because I've done it, I've got it off my chest.'

· Do you have any good kitchen cheats? Let us know on the food blog

· Delia Smith, How to Cheat at Cooking (Ebury £20). To order a copy for £18 with free UK p&p go to observer.co.uk/bookshop or call 0870 836 0885