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You once said food is especially evocative in conjuring memories. Which dish brings back the most memories for you?
"Ice-cream. I grew up in Paddington, and every Saturday morning my sister and I had to go to Church Street market with my gran. In the morning we'd be dragged around there, but on the way back there was a snackbar that had won lots of awards for its ice-cream. It was run by a Sicilian family and I remember there were only half a dozen flavours.
"This ice-cream became a big reward for me; I could put up with going round the market in the morning for a coffee and vanilla ice-cream! That's one of my earliest, positive food memories."
You demonstrated recently to the Queen how to make ice cream with liquid nitrogen. What did she think?
"I think she might have been a bit nervous - I was stirring quite vigorously and some splashed over the bowl! But she seemed to be really genuinely interested. And Prince Philip got completely stuck in. It was quite funny. He'd enjoyed my Christmas special and actually said: 'This is really quite tame for you, isn't it?'."
There's such a huge interest in cuisine and TV chefs these days. Do you think we've reached a natural plateau, which means in order to be innovative chefs are relying on gimmicks?
"There's been a big growth in gastronomical congresses where chefs do demonstrations. These combine some of the biggest names in world cooking with young, up-and-coming chefs.
"Younger chefs get invited to do a demo and it's a really big honour. They'll think: 'I can't just roast some meat and cook a few potatoes. I have to do something more creative'.
"I think the risk is that chefs would much rather show an audience something that spins around, puffs up and then disappears, because everyone goes: 'Wow that's incredible!'. But that has a danger of overtaking the good old-fashioned 'does it taste delicious' approach."
Before receiving your OBE you joked with Ozwald Boateng that you're just a man "who chops onions". What will it take to make you feel you've really made it?
"Don't get me wrong - I'm not giving my OBE up for anyone. That was one of the proudest moments of my life. But someone was getting an award for setting up an orangutan sanctuary in South America, there was a chap whose charity raised a fortune for terminally ill children in Romania... What I said to Ozwald was: 'I'm chopping some onions and you're doing some knitting!'
"What I was really saying was that we were there for doing something self-indulgent, something we love doing. I felt a lack of worthiness at the time. But I've got it and I'm not giving it back!"
A term closely associated with your cooking approach is 'molecular gastronomy'. Does it still apply?
"The term was actually created by a woman who ran a cookery school in California and an Oxford-based Hungarian physicist. They wanted to hold a workshop where chefs and scientists could interact, but the Sicilian centre they had in mind ran workshops on cosmology and gravitational physics, and said it couldn't just call their course food science.
"So they said: 'If we call it molecular and physical gastronomy can we use the centre?' And the centre said yes. That's where the name comes from.
"Unfortunately, the term has become associated with test tubes and foams and warm gels and all that sort of thing. My style is just cooking. If we were going to be really pure about cooking then man would only ever cook on an open flame. But evolution, that whole process, has given us more tools in the box. We're combining creativity with modern technology to create something delicious."
So do you apply molecular gastronomy to meals at home with your wife Zanna and your three children, too?
"No. Mainly because of all the work that goes into it, and some of the kit - I think if I came home with a freeze dryer or with a vacuum oven, my wife wouldn't be very happy!"
You've said a night out for you and your family when you were growing up was a meal out at the Bernie Inn. Do you still get as excited about the homely classics as you do about your exotic menu?
"More so than ever. There are so many classics - a goldmine of British recipes that I didn't know existed. Going back to the Tudors and the Stewarts, Georgian times even; there was an awful lot of creativity and really exciting-sounding dishes. I'm as interested in that as I've ever been."
You're involved in Walkers' new nationwide Do Us A Flavour competition to create a new flavoured crisp and in the past have turned the expected on its head, creating a bacon and egg flavour ice-cream, for example. Do you think it's possible to do the same with fried potatoes - making them taste good with an unexpected flavour like lemon sorbet?
"I think somewhere along the line these suggestions are going to come up. Obviously there's a manufacturing process that has to be used. That's an exciting part of the process - seeing which combinations could be made to work."
What attracted you to the Walkers concept?
"The opportunity to create something which hopefully captures the imagination of the British public. It's the combination of trying to come up with a new crisp that's creative, feasible to produce, and tastes delicious. Surprising and delicious can always be a challenge, so I'm very interested to see how it works out."
All the latest on the world's youngest royals