Lena Corner meets the real-life Willy Wonka of west London

Some of our customers are addicted to these already," says Damian Allsop, handing me an espresso cup of the richest, gloopiest hot chocolate imaginable. Clearly it doesn't take long to build up a habit. Melt, a new chocolate shop in London's Notting Hill, has been open just over a week, and already customers are dropping in for a daily fix.

But this isn't your run-of-the-mill, pralines-and-cream chocolatier. Cocoa, in its various forms, is an obsession with Allsop. His hands are darkened with the stuff and his face smeared in it. He reckons he must eat about 400g a day. The centrepiece of Melt is an open kitchen which Allsop inhabits. He spends his days there dipping, tempering and tasting; he is, if you like, west London's very own Willy Wonka.

Melt is actually the brainchild of his business partner, Louise Nason. "I really wanted to open a shop that would appeal to all senses - smell, sight, touch and obviously taste," she says. For her, the most important thing was to have the kitchen built on site. "The chocolates don't come in from some factory in Swindon or wherever else," she says. "They move literally 10 yards from the kitchen to the customer."

Clearly her plan is working. Walk in off the street and the heady, sweet waft of Allsop's creations hits you immediately. "People come in and just stop, lift their noses and breathe in," says Nason. To enhance her customers' sensory experience further, she leaves her chocolates out, piled high on plates to encourage people to help themselves. "I can't bear it when I see chocolates lined up behind glass counters, or when they serve them in plastic packaging," says Nason. "I think you need to get near them, right up close, to see exactly which one you want." (omega)

And these are chocolates worth showing off. Barely am I over the threshold before Allsop accosts me with his jasmine-tea truffle. "These take five days to make," he says. "The jasmine tea comes from China; it's £140 a kilo." Then there are his passion-coffee bonbons. "They're time released," he explains. "First you get the passion-fruit flavours then, 25 seconds later, it takes you somewhere else when the coffee arrives." Or his praline-covered nuts: "These go from soft to hard. They play on the reverse of the classical truffle." As well as these, there are his pots of chocolate spread which can be melted for a fondue or, more likely, simply eaten straight out of the jar.

Allsop gets his chocolate from some of the best chocolate houses in the world, including Valrhona and Michel Cluizel. Most of his other ingredients are organic, seasonal and free-trade. As there are no preservatives, the chocolates have just a two-week shelf life. Contingency plans for what to do with potential leftovers were scrapped in the first couple of days when it became clear that far more, rather than less, were needed. But weirdly, the most important ingredient for Allsop is water.

"I was looking for a clean flavour - a way of making the chocolate taste as near to its raw form as possible and found that mixing it with water lets the true flavours out better than using cream." Apparently no one else in the world uses this technique and Allsop is now obsessively experimenting with different mineral waters to see which works best.

It's a process which takes the chocolatier's art into the territory of molecular gastronomy. Allsop explains how it's all about a delicate balancing act between liquid and fat and achieving a thing called "complete crystal melt" then stabilising it. It's high- precision work and temperature is crucial. Allsop no longer needs a thermometer; a quick dab on his chin and he can tell you exactly how warm any liquid of chocolate it is. Recently he's started using a seaweed base, which sounds unusual but is a stabiliser that the ice-cream industry has used for decades.

It's not surprising to discover that Allsop has 15 years' experience working in Michelin-starred restaurants around the world. After starting at the Hyatt Carlton Tower with the granddaddy of pastry chefs, Robert Mey, he worked with Gordon Ramsay at Aubergine and then at Locanda Locatelli. His technique is also influenced by modern Catalan cooking practices in which ingredients are analysed on a molecular level, which he picked up during a five-year stint at El Celler de Can Roca in Girona.

He and Nason seem to make a good team. Nason used to work at Christie's auction house, and has taken charge of the Melt aesthetic. The clean, white lines and elegant chandeliers, courtesy of Alex Michaelis of Michaelis Boyd, are offset by dark, jagged mounds of chocolate. And the packaging is, inevitably, immaculate.

Nason and Allsop are now planning tastings, cookery courses, weddings and, of course, there's the impending stampede of Easter. The open kitchen has proved revolutionary. In the run-up to Valentine's Day it enabled them to produce "fortune cookie" hearts where customers could write a note to their loved one and have it sealed within the chocolate. Allsop was turning out the hearts as fast as he could temper the chocolate. A row of seats opposite the kitchen provides Allsop with the perfect audience. Customers can sit and watch as he turns out stock for the shop in his one-man production line. Like a true chocoholic, he'll wax lyrical about his medium for hours. But don't get him going. Once he's started on the history of chocolate, the Aztecs, Montezuma and so on, there's absolutely no stopping him.

Melt, 59 Ledbury Road, London W11, tel: 020 7727 5030; www.meltchocolates.com

Damian Allsop's fresh mint truffle

Makes 20-30 truffles

For these recipes, I suggest using a quality chocolate such as Valrhona or Michel Cluziel. These are available from Melt or, for a wider selection, go to www.seventypercent.com.

For the ganache
300g/10oz whipping cream (35 per cent fat)
200g/7oz chocolate (70 per cent cocoa content)
40g/13/4oz butter
20g/3/4oz fresh mint leaves

For the coating
500g/16oz chocolate (65 per cent cocoa content)
100g/31/2oz quality cocoa powder (I'd suggest Valrhona )

Melt the chocolate. Bring the cream to the boil, add the mint and cover for two minutes. Blitz the cream and mint, and pour a third of it on the chocolate and stir well to form an emulsion (of mayonnaise consistency). If the chocolate goes thick and stodgy, add a little more cream and then continue mixing. Slowly add the remaining cream, then blend in the butter. Add a pinch of sea salt if you like.

Rest in the fridge until it's set (up to two hours). Then pipe on to boards covered with cling film or greaseproof paper, in whatever shape you like . Cover with cling film and place in the freezer for a minimum of two hours.

To coat the truffles, place the cocoa powder in a bowl. Melt the chocolate, then cool to 30-32C. Remove the truffles from the freezer, and coat with the melted chocolate. You can do this with your hands (gloved if you prefer) by scooping some chocolate into the palm of your hand, picking up a truffle and covering quickly by squeezing through your hands. Plop into the cocoa powder and shake well to cover the truffle before the chocolate sets. When all the truffles are coated, sieve the remaining cocoa powder away.

Place in a sealed container in fridge until they defrost. Leave out for 30 minutes before serving.

Chocolate soup

Serves 4-6
250g/8oz whipping cream
250g/8oz chocolate (70 per cent cocoa content)
250ml/8fl oz water (or fruit purée)
Melt the chocolate and place in a blender or bowl. Warm the cream, and, if desired, infuse with herbs or spices (mint, ginger, cardamom or chilli work well). Add a third of the cream to the melted chocolate and blitz or beat with a whisk until it becomes an elastic, shiny emulsion. If the chocolate becomes thick, add more cream and keep mixing. Eventually it should resemble mayonnaise.

Next, slowly add the rest of the cream and the water. It's important to go slowly, mixing all the time, to retain the binding properties of the emulsion. It will feel very thin, but keep slowly adding all the liquid. Rest in the fridge for an hour or two (or overnight). When ready to serve, blend with a hand blender or whisk to create a foam, and serve with ice-cream or fresh fruit, or just as a chilled drink.