It is quite thrilling for me to meet someone who knows even less about cooking than I do - especially when she is publishing her very own cookery book. The Duchess of Devonshire - for it is she - actually begins her Chatsworth Cookery Book with the words 'I haven't cooked since the war'. She says she would have liked to make that the title, but the publishers wouldn't agree. Her friend, the hairdresser in Chesterfield, told her that her writing a cookery book was 'a bit rich!' but of course it will be - being by the Duchess, it will sell like hot cakes.

Her last book, Counting my Chickens, a collection of her very occasional journalism, still sells 100 copies a week in the Chatsworth gift shop. Everyone who visits Chatsworth falls over themselves to give money to the Duchess. I went to her farm shop one weekend and was astonished - you drive through miles and miles of empty countryside and suddenly find the entire population of Derbyshire crammed into one tiny shop and fighting to pay £10 for a jar of mustard. Apparently, the meat is very good - though it isn't organic - but you have to trample over grannies to get your hands on a lamb chop.

You would think, wouldn't you, that someone with a cookbook to plug would at least offer you lunch? But when I went to Chatsworth all I got was coffee - albeit served by a butler - and a few of those ultra-posh biscuits that don't taste of anything. No doubt the recipe - or as the Duchess would say, receipt - is in her cookbook. Thus I was inclined to concur when she told me, 'You are such a sport to come from London' though I wanted to tell her it was more to do with salary than sport.

Anyway, she was friendly enough and let me linger in the corridor admiring the many rosettes she has won for her chickens. I particularly liked one that said 'Best Opposite Sex' and the Duchess's explanation: 'If the champion's a hen, then they give it to a cork, or if the champion's a cork, they give it to a hen.' The Duchess is seriously obsessed with chickens - she has kept them for 75 years - and her study is crammed with chicken ornaments, chicken paintings, chicken books and, of course, her favourite magazine, Fancy Fowl. She thinks it's a toss-up whether she prefers Fancy Fowl or The Goat Society's monthly journal, since Country Life has gone right orf. She likes the Spectator, and occasionally writes for it, but its chicken coverage is poor.

The Duchess loves telling everyone, especially writers, that she never reads. When asked to pick 10 books she would take to read on the trans-Siberian express, she ran out of titles after six, and one of those was Beatrix Potter's Ginger and Pickles which she calls the best book on retailing ever written (the moral is don't give tick, and don't eat the stock). But not reading is one of the Duchess's well-known amusing eccentricities, along with worshipping Elvis Presley, and buying all her clothes either at agricultural shows, Marks & Spencer, or Paris. She seems to be wearing agricultural show for my visit.

I keep meeting people who adore the Duchess - in fact, I've never met anyone who doesn't adore the Duchess, except possibly me. Maybe I'm allergic to Mitfords - I seem to have read a million books about them, and never get any fonder of their tiresome nicknames and 'teases', their awful braying self-confidence. Reading the Duchess's Counting my Chickens, I practically ground my teeth to stumps - she is so sure of her opinions, and so sure she is amusing.

However, today she seems less iron-clad than usual. Her sister's - Diana Mosley - recent death has hit her badly although it could hardly have been a surprise given that Lady Mosley was 93; but it still leaves a gap. They used to write to each other several times a week, sometimes even twice a day. The Duchess says that she never kept a diary because she wrote to Diana instead. 'Did you know her?' she asks eagerly. 'She was amazing you know, unbelievable, serene and beautiful till she died. She was ill for 10 days, I suppose she probably had
a very small stroke and sort of faded. Nevertheless, the loss is indescribable because I mean I'm 83 and she's been there all my life.'

In truth, the Duchess seems keener to talk about her sister than her cookbook, and it is with some reluctance that we eventually address the subject at hand. But it is going to be very difficult, I explain, given that I can't cook at all, and she hasn't cooked for 60 years. It seems to me that her only qualification for writing a cookery book is that she employs a lot of cooks.

'No, my qualifications for writing a cookery book are nil. But I am very greedy, so that helps!'

She opens the book at random, and we both gaze, mystified, at a page listing about 50 ingredients. 'These recipes do seem incredibly complicated,' I remark. 'Don't they!' she agrees. 'But I think when you actually get down to it, they're not so bad - it's a pinch of this and a pinch of that. I do hope they're not too complicated. Herv¿ Marchand, who is the cook here, is a real stickler for accuracy, so it's no good just saying for chicken soup put half a chicken and a carrot. He really puts down everything.'

What is her favourite dish in the book? 'Oh, what a question!' she cries, and there is such a long pause that I have time to wonder if she has even read the book. But then she says, 'I think there's something of my mother's which always goes down well because nobody's ever had it, which is oeuf mollet, with deep-fried capers. We were rather brought up on it - it was one of my mother's specialities.' So what is it? 'Well it's sorft, you know.' What? 'Like a hard-boiled egg only sorft, and you take the shell off - quite tricky sometimes. I don't think you or I could do it! And then you put butter and fried capers.'

Sounds feasible. This is not, however, typical of the recipes (sorry, receipts) in the book, most of which involve at least two pages of ingredients. Frankly, I can't imagine who will buy the Chatsworth Cookery Book. Or I can imagine who will buy it, but I can't imagine who will use it. Who, for instance, would devote four days to making 'Salmon gravlax and cheddar terrine with beurre blanc sauce' for 48 people? Or 'Seafood Bombe with Saffron Sauce for 50'? The Duchess adds a helpful introduction, 'Philip [one of her chefs] assures me that it is not difficult, and only a little practice is needed to make a perfect bombe.'

The book is full of sucks-to-you remarks of this type - an absolute classic is: 'To get a decent egg it seems to me that you must keep your own hens.' To make Devonshire cream you have to own a 'house cow' and break every food safety regulation going - only little people care about tuberculosis. For gulls' eggs you send the gamekeeper out in late April with instructions to collect only from nests that contain a single egg, and then you give them to the cook to cook. This is what the Duchess means when she says she likes simple food.

As a child, she says, she didn't actually learn to cook, but she used to hang around the kitchen hoping for a square of chocolate, and she used to watch her mother making bread (the recipe for which is in the Chatsworth Cookery Book). Her mother, Lady Redesdale, was something of a food crank - she hated white bread which she called 'murdered food' and insisted on making her own wholemeal. This was terribly rare in those days - for an aristocrat to cook anything, let alone bread - but the Duchess explains, 'She was before her time in many ways - it was part of her health regime. We were never allowed a doctor or anything like that - she believed in Swedish massage even when she broke her leg.' The Duchess is not so extreme - she would go to hospital if she broke her leg - but she rarely visits the doctor. 'People do seem to rush to the doctor for nothing, don't they?'

Anyway, the Duchess learnt to bake bread, but not much more, until she and her sister Diana and Sir Oswald Mosley went to the Cordon Bleu school in Paris together, before the war, 'because we thought we should learn to cook. We used to cook three courses and invite people for lunch.' Why did Sir Oswald go? 'Oh, he loved food.' But wasn't it quite unusual then for a man to learn to cook? 'Yes, for an Englishman maybe. But then he wasn't influenced by what was usual, if you know what I mean.' No indeed - I now have a delicious mental picture of Sir Oswald Mosley, in his black shirt and jackboots, throwing a hissy fit because his souffl¿ hasn't risen. But anyway, the Mosleys had little chance to practise their Cordon Bleu skills because they spent the war in prison.

The Duchess's star turn before the war was a very rich dish called Lobster Newberg. But then came rationing, and by the time the war ended, she was married and pretty soon moved into Chatsworth. At Chats-worth, the Duchess's contribution to cooking is to go to the kitchen every day except Sunday and discuss the menu with her chef, Herv¿ Marchand, and his assistant. She tries to warn him well in advance when there are, say, 24 people coming to dinner or a whole team of curators from the Getty Museum staying for a week. 'We have a diary so we sort of know what's happening, though it's never exact - it could be five people on their way to Scotland or something. But you get pretty adept at that, don't you? You can always make an omelette.'

'You can?'

'No, I mean the cook can. Though actually I can cook omelettes.'

The Duchess is quite a tough hostess: she has no sympathy with people who suffer allergies or are picky about food. 'I just think food's food and you either eat it or you don't. What I can't bear is people who turn round and say ,"Oh no, peaches don't agree with me" - don't you hate that? Why can't they just say, "No thank you". It's a damn nuisance. It's like - what are they called those people who don't eat meat?'

'Vegetarians?'

'Yes. Why can't they say, "No thank you" - there's always a bit of bread or something. I just can't be bothered to pander.' Surely she must have the odd vegetarian in the family? 'Not knowingly - I may have. But they'd know better than to make a fuss. If I'm served rabbit, for instance, at somebody else's house, I just say, "No thank you".'

The Duchess has an aversion to rabbit dating from her childhood - her parents believed in the laws of Moses when it came to food, and wouldn't eat anything that didn't 'divide the hoof and chew the cud'. In fact, she rebelled as soon as she left home and happily adjusted to pork, but 'not rabbit, I couldn't, ee-ugh!'. I asked if it was because she thought of them as sweet little flopsy bunnies, but she said, 'Oh no, I love shooting them! But I couldn't eat them.'

Where has she eaten best in her life? At her sister Diana's, she says, and also at her sister Nancy's - they both had wonderful cooks - and at her sister Pam's where Pam cooked and they ate in the kitchen, which was most convenient, says the Duchess, because the food was always piping hot. She remembers other grand houses where she ate very well - the Cholmondeleys, the Astors - but it is her sisters' food she keeps coming back to. Was she always closest to Diana? 'No, not always. I think in big families you chop and change your friends. Nancy was the one I adored when I was little, although she was 16 years older, and Decca [Jessica], of course, the next one to me. And then Diana.'

Does she think Diana had a happy life? 'Well, what is a happy life? What is happiness? It's an idea, isn't it, which hardly ever happens. She had some pretty awful times, as you well know. I mean three-and-a-half years in prison without trial was a pretty strange experience, and at the height of her beauty, but she had a kind of inner serenity which kept her going. She always had that. She was the most extraordinary character.' Does the Duchess feel she's had a more straightforward life than any of her sisters? 'Yes, much more... But we're getting away from food, aren't we?'

Oh bother food - we could be having an interesting conversation, especially as she is in such a strange, vulnerable, autumnal mood, but I dutifully return to my list of questions. Has she ever eaten a Big Mac? No - and never will now she's read the book Fast Food Nation. Has she ever eaten at a motorway service station? Once, and never again - take a sandwich. Sushi? Loves it - she had to get it for her daughter when she was ill and developed a taste for it. Could she bake a cake? 'Don't think so, it would come out very odd. But wait a sec - I suppose if you can read, you can cook, because you can look it up in someone like Delia Smith.'

Delia Smith is one of the few television cooks she has heard of, but she has no views on Jamie Oliver, Nigella Lawson and the rest because she has never watched them. However, she likes Rick Stein, because he came to Chatsworth and talked to her about eggs for his programme Food Heroes. She is, of course, an expert on eggs, but doesn't claim to have a favourite breed of hen: 'My grandson likes the White Leghorns because they have very bright orange yolks, and some people like the brown Welsummers because of the chocolate brown shells, whereas Americans will eat only white eggs - it's just fancy.' I asked if some types of egg were better for boiling and some for frying, and she said crossly, 'No - you're thinking of potatoes.'

Sometimes, the Duchess confides, she feels quite keen on the idea of cooking herself: 'When I go to Peter Jones cookery department, or Divertimenti, it makes you feel very broody, doesn't it - it makes you want to cook?'

'Not me, never.'

'Oh really, you don't? What an excellent person to talk about food with! Have you never been thrown on yourself to cook?'

'No. I don't think you need to if you live in London.'

'That's true - you can live on sardines, the best food in the world.'

'Not sure about sardines - but there are wonderful ready-made meals in M&S where you just put them in the oven.'

'Yes, they're so clever - I don't know why anyone bothers to cook. I wonder if people do cook or do they just buy cookery books?'

'I wouldn't have thought anyone could actually cook anything from the Chatsworth Cookery Book.'

'Oh dear, I'm so sorry to hear that.'

What will happen to the Duchess? Running Chatsworth is her life - but her job will end the day the Duke dies, and he is now very frail. Presumably there are plenty of spare dower houses on the estate, but it would be hard for her to live at Chatsworth if she were not in charge. She has a house in Mayfair, but no enthusiasm for London - she is a countrywoman at heart. The estate electrician who drove me to the station told me she has a cottage at Swinbrook in Oxfordshire where she grew up, and will retire there, with her chickens.

Who knows? Perhaps she will take up cooking again after a gap of 60 years.
And then we could have the Duchess of Devonshire's Cottage Cookbook, which might be good fun - and even, conceivably, useful.

To order the Chatsworth Cookery Book (Frances Lincoln) for £9.99 with free UK p&p, call The Observer book service on 0870 066 7989

The Duchess's mother

Lady Redesdale's, poached eggs with fried capers and parsley butter 'Worms galore, fresh grass, earth for dust baths, grit from the roadside and all else that goes with real free range and is the delight of the hen-who-has-everything. All these blessings are transferred to their eggs... proper shells and orange yolks'

This is a popular and easy-to-make first course, although it does require last-minute cooking. We serve it with brown bread and butter.
serves 6

6 heaped tbs pickled capers in vinegar

6 tbs clarified butter

55ml white wine vinegar

6 eggs

3 tbs chopped parsley

Squeeze out the excess vinegar from the capers and dry on a paper towel. Melt the butter over a high heat until smoking and fry the capers, stirring continuously, until brown and crunchy (about 5-7 minutes). Take off the heat, lift the capers out with a slotted spoon, and set aside. Set the frying pan with the butter to one side.

Bring 570ml/1 pint of water to the boil, add the vinegar and reduce the heat to a bare simmer. Crack the eggs into the water (cook three at a time) and poach for 3-4 minutes. Drain on to a clean tea towel, then place one on each of 6 small warm plates.
Reheat the butter, add the capers, then the parsley. It will snap and crackle for a few seconds; as soon as it stops, take it off the heat. Put a tablespoon of capers and parsley on each egg and pour over a little butter. Serve at once.