Sonny's, 94 Church Road, London SW13

Great, a local restaurant with a top-class chef and innovative dishes. So what's the problem? Terry Durack comes to bury the Caesar, not to praise it

It's known among restaurateurs as the Caesar-salad clause. You let the chef do whatever he or she wants, as long as they don't kill anybody, and as long as there is Caesar salad on the menu. That way, nobody dies, and everybody's happy.

The Caesar is international restaurant speak for something for everyone. Ever since Caesar Cardini tossed the first one together in Tijuana in 1924, this single salad has invaded menus all over the world, killing off the Niçoise, the Lyonnaise and the composée and establishing its own creamy, cheesy, salty, crunchy menu monopoly.

So here I am, sitting by the open fire in an ultra-comfortable, moderately chic Barnesy restaurant, looking forward to the cooking of new chef Helena Puolakka, formerly head chef of Pierre Koffman's La Tante Claire. The menu reads beautifully, running from "queen scallops, marinated anchovies, herb salad, beurre blanc" to "ballotine of chicken, pancake of chickpeas, wild mushroom and tarragon sauce". And there it is, the dreaded Caesar, offered up as a side or a starter. E tu, Sonny's?

It seems a betrayal of the chef's talents to make her deliver Caesar unto Barnes as well as her own, more intriguing offerings. Some would see it as a comforting reassurance that Sonny's isn't too high-falutin to look after the plebs. I see it as a sign that this restaurant wants it both ways (more Caligula than Caesar, in truth) and is torn between the new chef's potential and the old clientele's expectations.

The old clientele, it appears, isn't all that old. Sonny's is as much a first-date venue as it is a regular haunt for the area's professionals. Everyone seems tall and slender and good-looking, the women in fringed chocolate and the men tieless, with soft pastel pullovers slipped on over business shirts.

It's all very pleasing and professional; a long, low and lean space from a cheerful front room that is home to a more casual daytime café, past a semi-private room, through a cottagey wooden-boothed dining-room, to a sophisticated gallery that finishes with the afore-mentioned fireplace. I'm not sure that it all feels like the one restaurant, but that's not a complaint. Starbucks has isolated the so-called "third space" in our lives between home and office – and here it is, in ecru, eggshell, oyster or whatever else you call off-white.

If that sounds disparate, then the starters are even more so, appearing to come from two different kitchens. An escabeche of mackerel (£5.75) looks gorgeous, the fillet gleaming of skin and expertly manicured, scattered with carrot and tomato dice in subtle reference to the technique of marinating cooked fish and vegetables. A diced beetroot salad is a fresh idea, and a teardrop of beetroot purée and horseradish cream is duotone pretty. The dish is gentle, polite and pleasant, but lacks the punchy vinegar tang of a traditional escabeche.

Then it's a stacks-on-the-mill platter of "crispy pork belly" (£6.25) that looks like a poor relation. Two flabby slabs of pork lie on baby leaves with a good poached egg, pan-fried ceps, and a furl of crisp Melba toast, linked by a creamy dressing. There are no particular high points of flavour or texture. The escabeche wins fins down.

Another professionally crafted, refreshingly democratic wine list compiled by the increasingly busy Peter McCombie MW makes me glad I drink so much. At £22.50, a 1999 Domaine Heresztyn Bourgogne Pinot Noir is versatile enough to hit it off with both a slow-braised lamb shoulder with merguez sausage, kidney and couscous (£14) and grilled halibut with crunchy onion tart and sweet potato cream (£14.50).

School report: halibut is a hard-working, firmly cooked meaty fillet, with great folds of wilted spinach and a dreamy pool of sweet potato purée. It comes with a very strange biscuit-like board topped with rings of pale, uncaramelised onion. Could try harder.

The lamb can go to the top of the class. As comfy as a pot-roast, it's a perfect round of meat squatting on some quite delicious couscous, a grain that is rarely cooked as it should be. There's a soft crunch from tiny jewelled vegetables, a few token slices of paprika-spiked merguez, and the happy surprise of lamb kidneys. Will go far.

Pud is a raspberry soufflé (£5.50) that feels overcooked, with a thin-tasting scoop of fromage frais and white pepper sorbet. A golden glass of Vin Santo comes with cantucci biscuits (£6.50) – now that's what I call a pudding – although the biscotti have seen the inside of the oven for five minutes too long. Must pay more attention in class.

Sonny's is far better than an average neighbourhood restaurant, serving up a sophisticated dining experience to willing and appreciative loyal regulars. It's professionally run by staff who are friendly without fawning, and swift without being pushy. I like the space, the attention to detail, and the price levels.

Considering Helena Puolakka's pedigree, the actual cooking could be more consistent; a sign, perhaps, of working without all those hot-and-cold running apprentices of La Tante Claire. I can only hope that as she settles in and establishes herself more fully, that Barnes will learn to hail Helena, rather than Caesar. *

Tel: 020 8748 0393. Open Mon-Sat for lunch and dinner. Around £95 for two including wine and service