Tempo, 54 Curzon Street, London W1

There are so many rules in Italian cooking – so many rules. And if you are going to break them – by making risotto with the wrong kind of rice or by serving rigatoni with a meat sauce, for example – you will need a Papal dispensation. Which is why Italian cooking hasn't evolved. It's been hamstrung by tradition. Tempo, in London's Mayfair, is the latest restaurant to try and move things on a little. With a Japanese chef.

If French cooking is about drawing attention to the chef, Italian cooking is about drawing attention to the food. But if the Italian cooking is being done by a chef called Yoshi Yamada, well, people are interested. They imagine he might want to shake off the confines of tomato and tarragon. And they would be right. Even if he has trained in Michelin-starred restaurants in Sardinia and Florence.

Yamada's site on Curzon Street has been home to a little Italian restaurant for as long as anyone can remember. It's done its time as a Mom and Pop trattoria, with oversized pepper mills and oilskin tablecloths. But its latest reincarnation is all about light and space – with aquamarine seatbacks for colour contrast. With little art on the walls, and no opera in the background, there's nothing to distract the diners from the food.

And the waiter is excited about the new menu he's selling. The carpaccio section – which contains swordfish and venison – is actually Italian sashimi. Best not to call it that. Not authentic. But our waiter did. And he was right. The seabass is too thick to be carpaccio. And it isn't down to Yamada's knife skills. It is about getting the right balance of fat, acid, spice and salt. He gets it bang on.

I'm used to a suggestion of fennel – like a touch of perfume on a pulse point. Something so delicate that I need to see it written down on a menu before I actually believe it exists. The fennel at Tempo comes in planks. But I like it anyway. Bundling it into my mouth with sea bass and grapefruit, I lose track of the individual flavours. And end up with one of those mouthfuls I will remember for ever.

The wonderful waiter then draws our attention to the chef's small plates (typically served in bars in Venice) called "cicchetti" (from £1.50-£4). The fatty tuna loin is heaped up on to a tiny bruschetta. Technically, it is "two bites big" and designed for sharing with friends. But sharing tuna this good would put a stress on any friendship. So I order a second.

The highlight is the lardo. Lardo is the butter of Italy – a cured pork fat, striated with rosemary. It's usually used for flavouring soups, but if you want to show an old-fashioned rusticity, serve it on its own. As I pop the bruschetta into my mouth, I regret everything negative I have ever felt about the Italians and their pedantry with food. Unfortunately, given the size of the bruschetta, that regret is only short-lived.

So I have high hopes of my Italian summer tomatoes (£6.50). Tomatoes don't taste like they used to. Their skins are bred for thickness to make them easy to transport. And they're never ripe – they are picked when they are green, moved to cold storage and forced to redness with ethylene gas. But Tempo douses my Italian summer tomatoes in balsamic, so that – even if they do taste different – I wouldn't know anything about it.

My pork belly (£14.75) is overdone and, instead of carrying just the right amount of butter-soft fat, is all crackling. Shame, because the oregano sauce served with it is begging for a warm, comforting strip of meat. And the crab, dill and lime sauce on the fresh tagliolini (£16) is just too darned mean on the crab. The same can not, however, be said of the dill and lime.

Food purists won't like the fact that – by pairing rabbit with pistachio, beef with hazelnuts and seabass with fennel – Yamada is breaking a few rules of Italian classicism. But hey. If we didn't break a few rules, we would still be grilling lumps of gristle over open fires. He just needs to make sure he gets the classics right too. If he does that, the Italians (and I) will forgive him anything.

Richard Johnson is founder of the British Street Food Awards (britishstreetfood.co.uk)

6/10

Scores: 1-3 stay home and cook, 4 needs help, 5 does the job, 6 flashes of promise, 7 good, 8 special, can't wait to go back, 9-10 as good as it gets

Tempo, 54 Curzon Street, London W1, tel: 020 7629 2742. Open daily, 12pm-3pm and 6pm-11pm. About £100 for two, including wine

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Reviews extracted from 'Harden's London and UK Restaurant Guides 2010'. www.hardens.co.uk