His Thai cooking is so good, he's even won over Michelin. So what's David Thompson's secret ingredient? A unique collection of authentic recipes. Michael Bateman tucks in

The sincerest compliment that has been paid me was from a very wealthy Thai lady," says chef David Thompson. "She told me she came to eat here wanting to complain, but she couldn't." A nice story, but Thompson's most high-profile pat on the back is a gleaming new Michelin star, the first in Europe to be awarded to a Thai restaurant.

The star has arrived improbably quickly. Nahm, his restaurant in London's Halkin Hotel, opened only last year. And Thompson is Australian, not Thai. Add that to our common conceptions of Thai food (rubbery fish cakes and sloppy green curries) and it seems amazing that he impressed the judges – ethnic cooking is not high on Michelin's agenda. But this is no ordinary Thai food.

Thompson, 41, first visited Bangkok when a holiday to Tahiti fell through. There he met Tan Ong Sak, his partner of 16 years, and stayed on for 18 months. It was Tan who introduced him to a cook he now refers to as Khun Yai, the Grandmother. "She was a dragon," he says. "She sent me to the market for ingredients at 6am, she had me pounding spices for curry pastes for half an hour at a time. But her food was incredible. She transformed my understanding of flavours."

While there he discovered the memorial books which families prepare when someone dies. "They include genealogy and tributes and, in the case of some of the women, a record of her special family dishes, often inherited. Most recipes in Thailand are handed down orally, so these written recipes are especially valuable," he explains. Bitten by the bug, he returned to Sydney and took a year's Thai language course.

David has collected 300 of these books, one of the largest collections. He began putting his knowledge into practice in Sydney, where his Darley Street Thai grew to become one of Australia's most praised restaurants. Last year, upon the invitation of the owner of the Halkin, he closed his doors and moved to London with a nucleus of his, mostly non-Thai, staff.

Thompson has also taken lessons from a cook whose mother had been born in one of the old palaces where they keep alive the tradition of court cuisine. "Thai royal cuisine is one of the finest in the world," he says. "It dates back at least 800 years. Thailand – formerly Siam – is a country that has never been colonised, and there is a continuing link through the royal palaces of elevated, refined cooking where nothing is too much trouble."

The cooking at Nahm is like no Thai food you have ever tasted. Certain ingredients are familiar enough – red chillies, coriander, ginger, kaffir lime leaves, lemongrass, Thai basil, coconut milk, sweet palm sugar. But they are lifted to another plane by the subtlety of the combinations. An appetiser called mo har is an example. Thompson minces chicken and prawns, combining them with chopped peanuts heated in a caramel of palm sugar, then seasons it with nam pla, a fishy soy sauce. He serves one mouthful on a juicy segment of mandarin, the other on a bite of pineapple.

It perfectly illustrates the drama of contrasting Thai flavours, textures and colours. Thai cooking is about living on the edge, he says. "I love the sense of brinkmanship on the palate. They take one flavour to an extreme but then balance it with another extreme." To make the point, he offers me a succession of dishes. Crab on Thai grapefruit (pomelo) with a caramel dressing, served on crunchy green betel leaves. Then a stir-fry of fungi and scallops, tingling with ginger, garlic, basil and white pepper.

Now he serves a green Thai curry with monkfish balls, the sauce smooth and rich with fresh herbs and keen green chilli. It contains two kinds of Thai aubergine, the larger one quartered and tasting sour, the others the size of marbles and bursting with hot bitter juice. An unfamiliar, dangerous flavour lurks in the background: blachan, the pungent shrimp paste that some Westerners find disgusting.

The spices and herbs are flown in weekly from Bangkok, along with unusual vegetables and fruits. "But you can buy adequate ingredients for Thai cooking in supermarkets here," he says. "And it would be folly to dismiss the excellent game, meat, seafood and vegetables in the UK." One example is the rare pork breed, Gloucester Old Spot. He partners it with smoked fish, green peppercorns, tamarind and eggs braised with star anise.

"I try to cook the kind of food you'd find in people's homes in Thailand, people with servants who can cook, dishes that are luxurious, elegant, lush and delicious," he says. "Purists may say some elements are not correct, and I'm at odds with their idea of presentation – carved fruit and vegetables. It derives from a tradition that in the kitchen nothing should be too much trouble, but to my eyes it seems contrived."

The Grandmother, like Thompson's complimentary Thai customer, would be proud.

Nahm, 5-6 Halkin Street, London SW1, tel: 020 7333 1234.