Janetira Thai, 28 Brewer Street, London W1(020 7434 3777). No booking. Meal for two £60
The night before I visited Janetira Thai for lunch I washed my hair. This is a big job. It requires an official notice to the water company and an amber alert from the Met Office. Still, I thought it necessary. If everything I had read was correct, I was going to be eating a dish of such uncommon chilli heat and power that my body was likely to deliver an involuntary response, far beyond the hiccups and pain most people associate with a major dose of capsaicin.
Many people sweat in response to eating chillies; few make like they've just been hosed down by the London fire brigade. Even if my tongue hasn't registered the heat my body will. The sweat flows from a well spring somewhere in the depths of my scalp, courses down the heavy geography of my face, pooling in the bags beneath my eyes, before spilling over on to my shirt. I reckoned it was worth starting that experience with clean hair. What's that? You're trying to eat while reading this? I do apologise.
I had heard mutterings about this particular dish online for a while. Then it was reviewed in a newspaper you do not and never will read, but whose critic has been known to follow my lead; I decided to return the compliment. It's not uncommon for a single dish to make an impact like this. People assume any buzz will always be around a whole restaurant, but it's not necessarily so. Sometimes it's the chilli crab at one place, or the whole roast chicken at another or the lasagne cooked to some porcini-heavy 14th-century recipe that you just have to try, because if you don't try it you are missing out. You are less than a complete person. I hate being less than complete. This me-too adventurism is both tragic and encouraging: tragic, because there is little sadder than doing something because you don't want to be left out; encouraging because what is life, if not a set of experiences accumulated?
Whether the mackerel curry at Janetira in London's Soho is an experience you will wish to accumulate will be a judgement call. I'm glad I've done it. In the way of this particular dish I suspect I will be compelled to do it again, even though to the western palate it is more wrongness than you could find in the locked bottom drawer of a Tory MP's filing cabinet. They make much of its heat. It is listed not just on the menu in the simple dining room, a vaguely gloomy modernist space of blocky dark wood tables, but also on a blackboard, where is written: "Super Duper Spicy – we dare you." There are four chilli pictograms by it. You get the idea.
Curiously, heat is not really the issue. That's a tiresomely macho sideshow. What matters is the flavour which is achieved – and there's no polite way to say this – through the use of fermented fish guts. Of course, fermented fish matter in the form of fish sauce, or nam pla, is a staple of Thai cooking. But this is something else, so very much deeper and darker.
The curry arrives at the tables a scary, rotten, vegetal brown, with the only hope lying in a couple of green beans bobbing on the surface. I stick my face into it and inhale. The thing honks. It is the profane realised in calories, an invitation to depravity. There is a kick of the Marseilles docks, with a heavy back note of Peckham drain and yet something else altogether more savoury and enticing.
The key to the dish is not how it smells, but how it tastes. Yes, there is heat. Eventually my diaphragm will indeed go into spasm and my hair will become damp and matted. But before that there is an overt, fishy savouriness; layer upon layer of umami which makes it irresistible. It is a deep well of flavour into which I cannot resist falling. I know it will repeat on me for days, that it will be inescapable. And even though, after a few spoonfuls, I move on to try something else, it is a dish I cannot help returning to. It cannot be denied. I need another hit. I'm glad I came.
There is a brighter, fresher edge of this overt fishiness in a green papaya salad with pickled tiny crabs called som tum poo (oh stop sniggering at the back there). Other things are far less challenging. Their moo ping, pieces of pork marinated in coconut milk and lemon grass and then chargrilled, are dark and smoky. They bring the flavour of the street indoors. More subtle are son-in-law balls, which have to be ordered by dint of name alone: halves of egg boiled until the yolk is only just set, then deep fried in a little batter and topped with crisp shallots and a tamarind sauce. It starts as a textural thing, before slapping you about the chops with a hit of sweet and sour. Ka nah crispy pork brings thumbnail-sized pieces of deep-fried belly, hinged between soft fat and splintering meat, with lots of invigorating greens and fresh red chillies.
Most soothing of all is their duck noodle soup. The soft slices of long-braised duck are great, as are the extra thin egg noodles with just a hint of bite. But it's the liquorice-dark broth with its hit of five spice that really makes its mark. It's what pho wants to be when it grows up. After the carefully choreographed violence of the mackerel curry I regard this broth as a place of safety. Most of the main dishes cost between £8 and £9, with a couple in the low teens.
For the sake of doubt this is a positive review. Janetira serves brilliant Thai food. It's just not the Thai food most people are used to. It does not make its point through lashings of sugar. It embraces pungency and depth. Some people may run from it; I ran towards it, my clean hair trailing in the wind behind me. Dessert starts and finishes at ice lollies, so instead we wandered round the corner to Spuntino and pulled up a stool at the counter for its brown sugar cheesecake and its peanut butter and jelly sandwich, made with an iced peanut butter parfait cut into white bread squares. That, and a big hit of properly made espresso, and the world settled at last on its axis. By the end of lunch my hair was dry once more. We were done.
Jay's news bites
■ The repertoire at Kaosarn in the covered arcade known as Brixton Village may not be quite as challenging as that at Janetira Thai, but the food is head and shoulders above much of what's available in Britain. Try the deep, dark soothing massaman curry, the sprightly larb salad, or their Bangkok style noodle soup, a real sinus opener. Queues build up at busy times, but it's worth it.
■ Proof of just how robust the British steakhouse business has become: the London branch of Palm, the glossy Stateside steakhouse chain, which opened in Belgravia five years ago, has finally closed its doors. It might have helped if they hadn't attempted to get away with charging £6 for chips. Meanwhile the all British Hawksmoor steakhouse group has announced a new branch on Yeoman's Row – five minutes' from where the Palm used to be. thehawksmoor.com
■ Spotted in a parade of shops fringing the lovely Hanger Lane gyratory system: the Golden Empire Restaurant which apparently serves both 'Polish and Chinese' food. No reference to the Chinese food on the website but they assure me by phone that it's true. Reports, please. thegoldenempirepolishrestaurant.co.uk
Email Jay at jay.rayner@observer.co.uk. Follow Jay on Twitter @jayrayner1
