Islington might be a byword for north London middle-class smuggery, but one thing N1 residents can't feel too smug about is the local food scene. There can be few areas which offer so many restaurants, and so few decent places to eat. Since the demise of Granita, where the Blair/Brown deal was famously (and it turns out mythically) struck, there hasn't been a new arrival to generate more than local interest. Ottolenghi is clearly fab, but not suitable for all occasions, or pockets.

But then, miraculously, creeping on to the scene with barely a whisper of pre-publicity, came Trullo. A neighbourhood Italian, serving simple, affordable River Café-style food, at a fraction of the price.

Word spread like bushfire. First came the bloggers (enthusiastic). Then the reviewer from the Evening Standard (ecstatic). Then, galumphing along behind them, the rest of north London. Which would be fine, if it weren't for the problem that a 40-cover restaurant can only hold, at best, 80 people a night. And far, far more people than that wanted to get in.

Including us. Our dinner at Trullo, suggested by an eager local friend, needed to be planned like a military campaign, with dates and babysitters ring-fenced weeks in advance, and a table finally, triumphantly, secured for several weeks ahead, albeit for a 7pm sitting.

The tiny Highbury Corner premises, once the home of the Gill Wing café, have apparently been given a makeunder; spartan décor – exposed ducting, industrial lights and rough-hewn shelving holding spotlit crates of produce – seems distinctly less smart than I remember.

The buzz, though, is phenomenal, a happy Highbury hubbub rising, over the course of the evening, to a din. To have secured a table is clearly cause enough for jubilation. But to eat the dishes produced in Trullo's tiny kitchen is very heaven. Mussels and slices of Amalfi lemon, crisp-fried in the lightest polenta crumb; grilled quail, the meat pink and sweet under smokily charred skin, with a silky roast pepper aioli; chilli-hot rump of lamb, grilled over charcoal and lapped by creamy, rosemary-scented white beans; a glistening, chargrilled mackerel, lightly pink at the bone, with Castelluccio lentils. We could have been eating in that perfect, elusive little Tuscan trattoria Islingtonians dream of finding on holiday, if it hadn't been for the London buses trundling past outside.

The men behind this dream of a local have both stepped from a wider stage; co-owner and restaurant manager Jordan Frieda (son of Lulu and John Frieda) is a River Café alumnus, while chef Tim Siadatan was one of the original intake of jobless teenage trainees at Jamie Oliver's Fifteen, as chronicled in the TV series Jamie's Kitchen. He went on to work in St John, and has clearly inherited the River Café philosophy – daily-changing menu inspired by the market, big bold flavours, superb ingredients simply presented – from his mentor Jamie.

Hugely to the credit of the Trullo boys, given the demand for tables, they have managed to keep prices incredibly low; starters and pasta dishes are £5.50-£7, main courses £13-£15, and puddings – including a nut-rubbly chocolate/pistachio cake – £4.50/£5. And in a freakish departure from the London norm, wines are marked up by no more than £10 a bottle.

That happy experience at Trullo prompted a revisit, a week or so later, to Fifteen, where – as the TV commentary would run – Tim's journey began. The last meal I ate there, a few years ago, in the zoo-like trattoria upstairs, was dispiriting; but on the evidence of a return visit to the downstairs dining room, the kitchen, now training its ninth intake of student chefs, is capable of some really excellent cooking.

A recent, low-key refit has seen the original space-age design of the restaurant softened into something more in keeping with the lovely old Shoreditch warehouse which houses Fifteen. The menu, too, has been rejigged, from a fixed structure to a more flexible one.

Umami-rich white risotto with truffled pecorino, anise-fragrant braised pork, almost oriental in its spicing, slow-roast shoulder of lamb in an anchovy-pistachio dressing; all knock-out dishes, from the same bold, Tuscan-inspired school as Trullo, if notably more fancy. The restaurants may share a postcode, but Fifteen's clientele is very different; not many casually-dressed locals in statement specs, but plenty of tourists and dressed-up couples celebrating special occasions.

Our dinner for two at Fifteen cost almost as much as dinner for four at Trullo; the steep pricing may be the reason that Fifteen has never really registered as a destination restaurant, other than for out-of-towners. Which is a shame – it deserves to get credit for its good food, as well as for the good work it does. Still, all profits go to the Jamie Oliver foundation, which has so far turned 95 jobless young Londoners into chefs at Fifteen, including one who has gone on to open the hottest restaurant in the neighbourhood. And that really is something to feel smug about.

Trullo, 300 St Paul's Road London N1 (020-7226 2733)

Food 4 stars
Ambience 3 stars
Service 4 stars

Around £30 a head before wine and service

Tipping policy: "No service charge. All tips go to the staff"