One evening recently, for the first time in almost 15 years, I was faced with a particular professional dilemma. Should I tell my wife [that’s me, JR]  that the restaurant we were heading off to for a long-planned dinner with friends was the same restaurant I had had lunch in earlier that day when, with only half an hour’s notice, it had been revealed as my host’s choice for a quiet business chat or should I say nothing? I plumped for honesty and we spent the rest of the journey whetting our appetites with my resume of an extremely accomplished lunch and three glasses of well chosen wine.

Our destination was Roussillon in the quiet residential area just off Pimlico Road, London SW1, wedged no more then five minutes' walk from the much busier Sloane Square in one direction and Victoria to the other. Here, chef Alexis Gauthier and his partners, James and Alexander Palmer who started and then sold the New Covent Garden Soup Company, run one of the most under-appreciated restaurants in the capital.

Gauthier, 31 who hails from Avignon,  Provence, (the restaurant is named after the village in the Lubéron rather than the Catalan region) chooses to operate along  unusual lines. Many French chefs who aim for the highest standards and achieve a Michelin star, as Gauthier did in 2000, tend to construct their menus around a core number of  dishes and see their role as ensuring that these dishes are executed with the same finesse regardless of fashion or season.

Gauthier takes a more Californian, even modern British, approach allowing the seasons and his suppliers to influence and determine what he and his obviously talented brigade cook with a particularly strong, and rather un-French, emphasis on the freshest vegetables and salads. My last meal at Roussillon, before this double helping, was 15 months ago just before Gauthier’s slightly esoteric menu constructed specifically for the nearby Chelsea Flower Show was on offer which included a green chlorophyll risotto and sautéed stinging nettles with scallops.

Since then, thanks to a clever paint job using mainly white, aubergine and mustard, the dining room has taken on a more distinguished look while the bonus, a large bay window, bathes the room in daylight and allows views of the St Barnabas church across the road. What is also striking is the simplicity of the table settings. A white plate and side plate, a bread knife, a salt and pepper set and a water and wine glass are all that encumber it  - the appropriate cutlery only comes as your next course is served.

And, as with my last visit, there was the same paucity of lunchtime customers. Our table of two aside, there was one couple, one lone diner and two businessmen including a Frenchman who spoke loudly and enthusiastically of his forthcoming sailing trip round the Cape of Good Hope but still did not manage to put me off my food.

Caught in the dilemma of lowering prices to bring in extra lunchtime trade or maintaining standards, Gauthier chooses the latter option with a menu at <sterling>30 for three courses while ensuring that his kitchen keeps as close an eye on the clock as his customers.  The first of our three courses, prefaced by a stunning amuse bouche of  poached red and yellow carrots with chicken jus and shavings of white truffle (currently 3,600 euros a kilo and rising!) and including a disappointing pre-dessert, appeared at 13.10 with the coffee being served at 14.15.

During these 65 minutes we also enjoyed a choice of eight different breads, including miniature baguettes with such pointed ends that they could have doubled as chopsticks; a salad of seared scallops with ginger; a bowl of glistening, unctuous cepe risotto; a couple of crisp fillets of red mullet with glazed parsnips which made and unusual but effective partnership; and what were described as ricotta gnocchi but had in fact been so overworked that they had become too soft and lacked any distinctive texture.

Initially, I rather resented the speed with which my host plumped for the roasted black figs with fig and honey ice cream and French toast  because it left me no choice but to order the chocolate and praline finger (the exceptional cheeseboard would have to wait for dinner). But now, having tasted one of the most sublime desserts in London, I am extremely grateful. This four inch stick of chocolate and praline covered in glistening room temperature chocolate (a sort of heavenly Crunchie bar) has the most delicious crunch and texture with, because of its high quality ingredients, a clean rather than a cloying finish. Any manufacturer of up market chocolates would be well advised to taste this and see how Gauthier’s creation could be made available to a much wider market.

Seven hours later I was able to use this insider knowledge to great effect as our even more impressive dinner came to the dessert stage.

Initial ‘amuses bouches’ included chickpea beignets to be dipped into a seed mustard sauce and bite-size mouthfuls of crayfish, cucumber and pickled ginger before a repeat of the white truffle shavings, this time on top of a cauliflower purée. Stronger flavours were then unleashed in a dish of roasted baby beetroots, bean sprouts and red chard with albeit too little cider vinegar and a truly autumnal thick soup of chestnut and pheasant ladled from a gleaming copper pan that took my French guest right back home in its presentation, style and flavour.

What distinguished the main courses was not so much the quality of the wild sea bass, the Donald Russell Angus beef, or the milk-poached smoked haddock as their unusual but hugely successful vegetable accompaniments in particular. Salsify added crunch to the bass while a combination of Jerusalem artichoke and Parmesan lifted the haddock and, equally gratifyingly, both are fiddly vegetables whose preparation is best left to professional kitchens. The greengage and almond tart and salty shortbread with apple and mascarpone sorbet were also very good even if neither will achieve the cult status I foresee for the chocolate and praline finger.

Minor reservations aside, most noticeably the gnocchi and the fact that the sea bass was not on the bone as advertised, these were distinguished meals whose pleasure was enhanced by thoughtful, attentive service, a well chosen,, sensibly priced wine list and the realisation, perhaps of less comfort to Gauthier and his partners, that Roussillon is an increasingly rare example of an individual restaurant. It is not part of a group, big or small, nor is it attached to an hotel or financially supported by a larger, less expensive brasserie.  My only professional disappointment was noticing empty tables on a Thursday, usually the city’s busiest night of the week. Gauthier and his team deserve to be playing to full houses.

Roussillon, 16 St. Barnabas Street, London SW1W 8PB, 020-7730 5550, www.roussillon.co.uk .

Lunch Wednesday-Friday; dinner Monday-Saturday.