From mothership Zuma has emerged a new satellite restaurant - powered by a robata grill. Sharp and contemporary, Roka is Japanese, but not as we know it

If I tell you about the ice at Roka, you'll think I've been drinking. It's beautiful. The bartender works with a huge block of crystal-clear ice, a number of surgical-looking carving implements and a variety of squat glasses, to design the right ice for the job. It is at once a very fashionable, futurematic approach to ice, and a return to classic, old-fashioned bar-tending skills.

A glass of cooling plum-infused shochu (£5), for instance, comes with a single, sculptured ball of ice as big as a scone that snap-chills the vodka-like spirit without watering it down.

The ice is made from purified water, which has been cooled down slowly over four days, the temperature reduced by degrees to prevent the ice cracking or clouding. It is so clear that once dropped into a clear drink, it simply disappears. Think of all the cocktails you have had ruined by melting ice, and you will realise why I'm still blathering on about it. It's the Romanee Conti of frozen matter.

Roka is already known as Baby Zuma, being the younger sister of Zuma, Rainer Becker's ridiculously popular and pricey sushi-stop in Knightsbridge, but it has different claims to fame. The first is the central hearth of the restaurant, the robata or charcoal grill, and the second is the warm and woody downstairs bar known as the shochu lounge, overseen by the respected mixer and fixer Tony Conigliaro.

The attention to detail here goes way beyond the ice. Take the decor, another super effort by Japan's Super Potato design group. The large corner room is encased in floor-to-ceiling glass, all action arranged around the robata. A mass of contrasting textures and tensions, there is a wall of rustic stone, one of hand-painted Japanese paper, and one of nothing more than precisely stacked reams and reams of paper.

Around the grill, Kiwi head chef Nic Watts and his team tend the coals (the grill uses only bincho tan charcoal from Wakayama near Osaka) surrounded by a broad sweep of brown wooden bench and further flung bare brown tables.

The do-anything-for-you staff are chicly tunic'd and the crowd is a hubbub of flippy blondes, celeb Lebs and slightly manic PRs and PAs who have strayed over Oxford Street and think they are near Camden.

Robata grills lead the menu, but there are choices in sashimi, salads, sushi, skewers, soups and so on as well. Small pork and scallop gyoza (£6) go well with a shochu aperitif, being loosely furled, cutesy-pie parcels of silky dumplings, the filling a pleasant mulch and the bottoms correctly scorched to a crisp.

Being mad about daikon (also called mooli or white radish), I'm a sucker for a dish of daikon braised in miso then finished on the grill (£4.30), which caramelises the natural sugars in the fermented soy-bean paste until they taste like candied yams.

Then, more thrills from the grill in the form of four lamb cutlets (£15), marinated first in fiery Korean spices then grilled until charred, glazed and sizzling. The chops are inconsistent in tenderness, but the flavours are hotly compelling.

The wine list wends its way through New and Old worlds with confidence, and the soft rich fruit of a Domaine de Gry-Sablon Fleurie 2003 (£25) carries the spice of the lamb as if born to it.

Another dish to add to my list of new best friends is kani no kama meshi (£11), a rice and crab hot pot that arrives at the table in its iron pot, neatly encased in a timber frame. A fluorescently green mound of wasabi-flavoured tobiko (crunchy flying-fish roe) is stirred through the light, soupy rice - this sounds awful, doesn't it, but it isn't - so that every mouthful has the sea sweetness of crabmeat and the titillating crunch of the prickly little roe. What a stunner.

Not everything is so stunning. A spinach salad (£4.90) is as insipid as any salad of that most insipid leaf, baby spinach, and there seems no rhyme or reason for the pacing of dishes, which makes it hard to order a meal that has any logical sense of progression. A dish of prawn, cucumber and chrysanthemum maki roll (£6) comes last, and is dull and bland. Dessert, of a weakly flavoured pomegranate jelly with a slightly slushy lychee sorbet (£6.30), seems merely to be going through the motions.

Baby Zuma is more casual and more fun than Mother Zuma, with an emphasis on grilled-to-order food, bistro energy and friendlier prices. The real context, however, is much wider, taking in any and every attempt to modernise food in this most conservative of societies.

Mastermind Becker knows just how to make Japanese food ultra-sharp, contemporary and fashionable, without compromising flavour or consigning integrity to the past. He's going to be hugely influential as we continue to shed the suburban faux-French sway that keep most of our cooking conservative and mediocre.

It's hard not to fantasise that this - kim chee, yakitori, edamame and salmon teriyaki - is what we will be eating in the cardboard cities of the future, and that shochu will be the only drink in town. Let's just hope we can still get ice.

15 Roka 37 Charlotte Street, London W1, tel: 020 7580 6464. Open Monday to Saturday for lunch and daily for dinner. Around £85 for two including wine and service

Scores 1-9 stay home and cook 10-11 needs help 12 ok 13 pleasant enough 14 good 15 very good 16 capable of greatness 17 special, can't wait to go back 18 highly honourable 19 unique and memorable 20 as good as it gets

Second helpings: More chefs on view

Moro 34 Exmouth Market, London EC1, tel: 020 7833 8336 From the open kitchen at the back of this warm and woody Clerkenwell restaurant, Sam and Sam Clark and their team turn out an ever-changing menu of North African and Spanish-inspired dishes that are as moreish as they are Moorish, from warm octopus and potato salad, and wood-roasted pork with runner beans and piquillo pepper sauce, to yoghurt and pistachio cake.

Fourth Floor Café Harvey Nichols, 107 Briggate, Leeds, tel: 0113 204 8000 This bright, smart café with its views over the rooftops of Leeds has wasted no time in establishing itself as something of a lunch hot spot. Flanked by the open kitchen on one side and a slinky bar in the other, it's the perfect showcase for Richard Allen's colourful and contemporary modern bistro cooking, ie roast halibut wrapped in Parma ham, linguine with crab, and scallops in saffron risotto.

Firehouse Rotisserie Anchor Square, Bristol, tel: 0117 915 7323 Located in a restored leadworks in Bristol's Harbourside Millennium development, the Firehouse, naturally, specialises in pizza from the brick oven and roasts such as herbed chicken from the rotisserie. Wrought-iron chandeliers and iron girders may hark back to its industrial past, but the open kitchen is the last word in corporate transparency.

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