The Wild Gourmet

The name Wahaca comes from the phonetic spelling of Oaxaxa, a region of Mexico famous for its food markets. The dishes are healthy but hearty (the corn tortilla is gluten-free). And the restaurant's unique selling point is using fresh ingredients from English producers - Lancashire cheese, peppers from West Dorset, chillis from Devon. Everything is scrupulously "sourced" from sustainable fisheries and free-range piggeries.

To make sure the dishes worked, she invited her many chef friends for tastings-Nevertheless, when the first customers came flooding down the stairs it was a terrifying moment. "I wondered how we were going to feed them all." Now of course even her family can't get a table. Her parents booked five weeks in advance, then had to spend an hour waiting across the road at TGI Friday. "It was very democratic," she laughs.

It has taken two years to build up a kitchen team. "It's crazy to expect a new restaurant to have perfect food when it opens. Though I do get cross when the reviews say 'Why don't they have traditional food like chiles en nogada?' which is totally out of season now. I feel like saying: 'Get your facts right, mate.'"

Miers has been frantically scouring London for Mexican-born staff. " Hopefully the embassy will be helping us find chefs." There's a real hotchpotch of nationalities behind the scenes. There have been a few spats as not everyone wants to work 18-hour days. Another man who just came for a trial lodged a complaint about the state of the kitchen. Miers is quivering with indignation.

She is the executive chef and co-owner along with Selby, but not too proud to scrub down tables. And, for a gentle soul, she admits she can be "ferocious" in the kitchen. She comes from the right side of the tracks, of course. Privately educated at St Paul's, she speaks Spanish, French and Portuguese. Guests at her book launch for Cook last year included Flora Astor, Alex Spencer-Churchill and Hugh Fearnley-Whittingstall. But Miers is engagingly modest. "Sometimes I feel a bit of a fraud in front of my cheffy friends. I'm basically a cook. Best friends of mine have worked at Moro and St John and for years I lived with chefs from The River Café. They are all properly trained chefs, who aren't just about TV. I can't help feeling I've taken a bit of a shortcut."

She has cooked since she was seven, but it never seemed a proper career. "My school was academic, and I put extra pressure on myself because that's the sort of person I am. Plus my father was keen that I went into the City. In my head I was thinking 'Why not? If you've got the luck to go to a good school, and be well-educated, then you should really do something proper with it.' So I guess that's what tortured me for a while."

Reading between the lines Tommi (as her friends call her) had a bumpy adolescence. At 11 she had a punky haircut and was wearing the tiniest of mini skirts. By 15 she was out drinking until all hours. She kept her head, but she wasn't happy. After A-levels she did a gap year as a VAT consultant for nine months. "That was really horrendous. I think my father bullied me into going for the interview," she laughs. "He thought it would be good practice for Oxford. I was so laid back that I think they thought 'This girl is cool as a cucumber: we want her!'"

Pretty quickly she realised she didn't want to be in the City "which left a bit of a vacuum because I'd always assumed I was going to become a stockbroker". Then to her shock she was turned down by Oxford. "I was quite arrogant in those days. I thought I'd just walk through it and didn't do any work. I did a laughable interview. I was all over the place."

There were extenuating circumstances. Her twin brother had been diagnosed as schizophrenic, which understandably became the main family focus. "I was very good for ages, then suddenly at 18 I decided I was fed up with being good. I did a slight bomb-out. I had always been the saviour of the family. Then I started getting it all wrong, and they were like: 'Hang on, now the whole family is disastrous. What are we going to do now?'"

She ended up studying languages at Edinburgh, but hated it. After college there were stints in advertising and marketing. She worked on Money Week magazine for a while, modelled and helped in a clothes shop. But nothing inspired her.

Then she met Clarissa Dickson Wright, when they were both modelling in a Countryside Alliance fashion show. Dickson Wright advised her: "Doing what you're passionate about is the only way to enjoy life."

She persuaded Miers to sign up for the Ballymaloe Cookery School in Ireland. "In my head I assumed fluffy public school girls went into catering - I've since found out it's an incredibly tough industry."

Ballymaloe changed her life. "I was happy, genuinely happy, for the first time in years. I knew I was on the right path." After the course she stayed on in Ireland working for a family of cheese-makers. "I was making cheese by the sea, so I could walk and get fresh air." She and a friend travelled round markets and made bread and pasta. "It was very Famous Five. But I was doing things because I wanted to, not because I thought I should."

Returning to London, she helped set up Villandry's market stalls, and she and a colleague put together the Soup Kitchen book of recipes by top chefs (with profits going to the homeless). Then a friend asked if she'd like to run the bar at a start-up restaurant in Mexico City. "I spent five days learning to making cocktails with my friend, Jasper Ayres, whose mother used to run the Groucho Club. Then I had one night working in a London bar before I flew," she laughs.

Running the Mexican bar was fascinating, back-breaking work. Afterwards she spent six months travelling around the country, pinching menus, exploring markets and cooking. She even persuaded Diana Kennedy, the doyenne of Mexican cookery writing, to see her.

Back in London in 2005, she had no job, no boyfriend and huge debts. "I was 29 and going nowhere." She entered Masterchef "for the ride" - and won. Miers is certainly not your typical fame-hungry TV star. But she charmed judges John Torode and Gregg Wallace with her brilliant but eccentric cooking. "That girl has fruit coulis pumping through her veins instead of blood!" Gregg observed.

Part of the prize was six months in a proper chef 's kitchen. She was offered Le Gavroche but a friend told her she'd hate it. She went along to Skye Gyngell's Petersham Nurseries and fell in love with the restaurant.

Rather than making her do a brutal apprenticeship, Skye put her straight on pan-frying fish and meats. "I was literally at her side. If you do the traditional chef 's training in a big kitchen, you're peeling potatoes for two years. Though I'm sure I could have learned a lot from doing that," she adds, slightly wistfully.

She loves the "magical" ritual of food, the way it brings people together. Her own family is very close-knit. "A boyfriend once complained I was still attached by the apron strings." She is touchingly protective about her twin. "He doesn't work, he just hangs out and teases me a lot." And she reveals that her grandmother was mentally ill. "There's quite a strong strain of it in our family, so I guess it's something we've all grown up being aware of. In some families it gets swept under the carpet. I'm lucky because our mother has always been very strong about talking about emotions and confronting things."

Today Miers lives in Shepherd's Bush with her boyfriend. "He isn't a chef but he's wonderful with a very relaxed take on life. He teases me a lot when I'm very overtired, or too boisterous, which is great."

Cooking has proved her saviour. "Cook from the heart," she advises. "Put your heart and soul into it. You learn about food and you learn about yourself. When you're in your darkest hour, dig deep and keep going."

Wahaca, 66 Chandos Place, WC2 (020 7240 1883, www.wahaca.co.uk). The Wild Gourmets starts on 18 September on Channel 4 at 9pm.