Petit Pois Bistro, 9 Hoxton Square, London N1 6NU (020 7613 3689). Meal for two, including drinks and service: £75

Not long after the Petit Pois Bistro opened in Hoxton Square, London, word began circulating about one of the desserts on offer. When he heard about this, the head chef apparently let out a howl of despair. “Is this what I’m going to become famous for?” Chris Smith asked. “A chocolate mousse?”

Yes, Chris, I think it just might be. And rightly so, for it is a thing of true beauty and soothing darkness. It is chocolate mousse as balm for the soul. Chuck out the antidepressants. Cancel the talking cures. Just prescribe a plateful of this to the anxious and panicked. The world will immediately seem that little bit better. It manages to be both intense and ineffably light. It is chocolate mousse made by a man who knows exactly what the instruction to “fold in the egg whites” means.

It helps that it is served to you from a large ceramic bowl of the sort your mum used for mixing cake ingredients. It arrives tableside looking like a promise, the surface buried under a fresh snowfall of rust-coloured ground cocoa. Of course, there’s portion control, but in the serving method is advertised an authentic bear hug of generosity.

That describes the whole place. There is nothing especially original about the Petit Pois, including the name. There are restaurants with the same words above the door in Galway and Paris, in Nottingham, Puerto Rico and Charlottesville, Virginia. It intends to be nothing more than a clichéd French bistro, albeit one with a playlist of Tom Waits, Johnny Cash and Gordon Lightfoot. If they can growl, their voice can be played here. The menu is extremely short and built around one premise: if you’re not going to do very much, you’d better do it exceedingly well. It takes the clichés into which it has bought very seriously indeed.

And rightly so. Is there anything more beloved of the British middle classes than the French bistro? For decades in postwar Britain we had to make do with awful pubs full of glowering waiters and tortured vegetables and carpets that smelt of rotten cabbage and neglect. Or we had Wimpy bars and Golden Eggs, where the interest lay only in a tomato ketchup dispenser shaped like – get this! – a tomato, the spout blocked by a scab of a coagulated sugar, pulp and despair.

There was the trattoria boom in the 50s, but they were mostly about picking overcooked pasta from your teeth and laughing at pepper grinders that looked a bit like penises. In the 50s that was hilarious. (Still is, to be fair.)

The French bistros that started popping up in the 60s and 70s were the first attempt by British cooks to engage seriously with the cooking of somewhere else. They were a launch pad for the exotic, for the possibility that indulgence might not be a crime. For that we should give huge thanks. The Petit Pois honours that tradition. It is owned by the same people who have the award-winning bar Happiness Forgets, a space of darkness and whisky, which occupies the basement below. Start there in the downlit corners with a serious cocktail chilled with a block of ice the size of a house brick. Those cocktails are where their heart is, so watch them if you order a glass of fizz. They might attempt to mix the end of one bottle with the beginning of another. That will never do.

Afterwards, slip upstairs to the rugged, plank-ceilinged room, with its coffee-coloured banquettes, bare brick walls and filament lightbulbs. The menu may be French, but the room is pure Hoxton. There are roughly three choices at each course. One of those starters, a plate of blue cheese, walnuts and beetroot, feels more like an exercise in throat clearing than a real starter. It’s the only muted note. Moules marinière are plump and bouncy, rather than wizened, and leave behind a sweet-salty puddle of sauce that demands to be mopped up with their good sourdough, served warm. Thick discs of impeccable black pudding, dotted with pearls of glistening fat, lie under a poached egg with a liquid yolk and are surrounded by lardons of heft and seriousness.

Main courses, at £17 each, are the words “what did you expect?” in calories. There’s steak frites. There’s duck confit. There’s sole meunière. Which is as it should be. The steak is served perfectly medium rare, is thick cut and pre-sliced on the plate so you can see they’ve done right by it in the kitchen. Thin, skin-on chips did not come out of a bag, and rustle in all the right ways. There is a dish of frothy béarnaise made with handfuls of fresh tarragon and a serious bit of wrist action. You don’t just learn to make a béarnaise. You have to keep learning.

Duck is confited on site and is pungent with bay and star anise. It’s as fragrant as the perfume counter at Liberty’s. The skin is crisp. The meat falls away from the bone. A little white onion purée lubricates the plate on one side. A dauphinoise full of cream and garlic and largesse does the same job on the other. And the petit pois? They turn up as pea shoots. Some might roll their eyes at this, but I’m rather fond of a nymphlike pea shoot, with its sweet, grassy tones. We have a side salad of those in a honey vinaigrette and another of roasted onions, with more of the bruising lardons.

Other than the chocolate mousse there is a crème brûlée tart, and it is a good crème brûlée tart. The pastry is crisp. The crème is just set. The top is glazed. But I’m only telling you about this because I feel I ought to. It’s not the chocolate mousse, which is about the best three minutes you can have in London for a fiver right now. You can try to make it last longer if you like. Or you can just order seconds.

The wine list is short and mostly French, which again is as it should be. The risk here is that the extreme pleasure I took in the Petit Pois Bistro comes across as me selling it to you as some grand gastronomic experience. It’s not. Those places are just too much admin. In the way of the classic dishes of the French bistro the Petit Pois is much more elemental than that. They feed you well and they feed you carefully and they send you on your way. Which is what most of us want from a restaurant.

Jay’s news bites

■ Comptoir Gascon in London’s Smithfield is a French bistro which takes its classics very seriously indeed. Alongside starters of fish soup and charcuterie is a menu section entitled “The very best of duck”. It includes duck confit and a rather glorious cassoulet Toulousain, which will feed you for a week. At £14.50 it’s great value (comptoirgascon.com).

■ The charity Action on Hearing Loss has launched a campaign urging restaurants, cafés and bars to reduce background noise, including piped music. Their survey found that nearly eight out of 10 people had left a restaurant or bar because of excessive background noise (I am one of those eight). The problem is exacerbated by trendy hard surfaces (actiononhearingloss.org.uk).

■ The great Henry Harris, once chef-owner at Racine, will not now be overseeing the kitchen at the Dog and Badger pub in Buckinghamshire, as previously reported here. He’s left the project, citing “artistic differences”. Do keep up.

Jay Rayner’s new book, The Ten (Food) Commandments, is out now (£6, Penguin). To order a copy for £5.10, go to bookshop.theguardian.com

Email Jay at jay.rayner@observer.co.uk or follow him on Twitter @jayrayner1