There is one food guide that people in the restaurant business take seriously; the Michelin Guide. It commands respect because it's run by professionals and as far as anyone knows is impervious to bias. The accolade of a Michelin star is something most serious chefs aspire to - it's a marker, a symbol of excellence achieved. Ireland has two two-star Michelin restaurants, Thornton's and Patrick Guilbaud.

The eponymous Thornton's is in Portobello, alongside the banks of the Grand Canal. It has recently been re-designed and refurbished and I sat upstairs with Kevin enjoying the view over the canal. He's remarkably youthful looking for a man who runs a successful restaurant, a job I'd suggest is harder than most. He told me that his interest in food began as a boy, and then later his first job was running the vegetable garden in the Cashel Palace. He feels strongly that learning about every part of the process of getting food onto plates, from the garden to the kitchen, has served him well. The horticulture gave him an understanding of the seasons, a delight in using fruit and produce in its proper time, as well as the knowledge of how to choose the very best. 'Today people are used to buying food in boxes, pre-packed. When I grew up there were markets, you chose your produce. It's a shame we've lost that.'

Those early days must have made an impression, when I asked what the future might hold for him he looked wistful. 'Maybe a place in the country where I could produce everything I need for the kitchen. A place where I wouldn't have to rely on other people to produce the food I cook.' For the moment he's at the markets daily, looking for whatever is in season and good. A young son has him out of bed at seven in the morning, early enough for a man who rarely gets to bed before four. 'We cook breakfast together and then I take him to school. He's already learning his way around a kitchen. I try to get home and have a late lunch with him, and we all eat together in the evening before work.'

There's a tangible team spirit in Thornton's; I suspect no really successful restaurant could be without it. Getting the team right is vital, as Kevin reminded me 'you're only as good as the weakest link in the chain.' They all eat together before the evening begins. 'What we do here is theatre, and we share the meal before the curtain goes up at eight.' So who is the performance for? 'It's for people who care about what they eat. Everything that comes out of my kitchen is made from the very best ingredients I can source. People think I'm off my rocker getting my chickens from Bresse in France - they're ridiculously expensive, £26 a bird - but they have a real taste, as opposed to the birds from the batteries.' I wondered if he felt that there's a growing interest in food Ireland. 'There is, there's a growing awareness of food, but there's still little understanding of it. We don't have a culture of food. People don't cook on a regular basis, they watch chefs on TV or buy cookery books and look at the pictures. If cooking becomes a hobby, then it's not real cooking any more.'

Being consistent is the foremost of his aims. 'It's important, and that's why I'm here all the time. It's why McDonald's is successful, the food's not great but it's consistent. You have to try to keep the energy up throughout the night, right up to the last table. That's why the numbers are limited, you can only keep that energy going for so long.' For Kevin life is one long learning process, each period, each age, teaching him the skills for the next stage. 'I never look back at what I've done, I look forward to what I've still to do. I still want to learn, improve my skills.'

When work is this demanding, what does he do when he's not working? 'Well, on Sundays for instance, that's a family day. We eat together - I cook - and we walk, maybe in the hills or on the beach. I'm into photography at the moment, I enjoy it, it helps me unwind.' And holidays? 'We try to get away in August, but it's not easy. At Christmas, too, maybe skiing. I like water, surfing and diving.'

Kevin Thornton has a philosopher's take on life. Harmony, balance and organic growth form much of who he is and what he does. The energy that comes from his passion is transferred to his team and to the ethos of his restaurant. Perhaps we could call it 'energy food.'