Roganic, 19 Blandford Street, London, W1

Eating at Roganic is like a night out at the opera. But can it hit the high notes?

Were I to list the dishes I have at this week's restaurant, it would take almost all the available space, so I advise you to visit roganic.co.uk and read the menu. Better, click through the gallery – everything I eat is there in glorious detail (but be warned: you'll want scratch'n'sniff'n'tasteorama).

Dinner at Roganic is six or 10 courses, no substitutions (unless you're veggie), no menu even, unless you ask for it. So, you'll be saying "thank you" a lot. And you'll need to set aside an entire evening for the meal (I was there three-and-a-half hours); think of it as theatre.

This might just regain for tasting menus the kudos lost by too many places doing lacklustre examples. There's so much fun, imagination and skill involved that though a couple will be looking at a £200 bill, it's an evening on a par with posh tickets for the Royal Opera House. There's a similar sense of "hot ticket" about Roganic as there is of a stellar casting in theatre or opera. Simon Rogan (pictured) is chef/patron of the acclaimed Cumbrian restaurant L'Enclume – and this Rogan/ organic offshoot is a two-year spin-off.

There's much debate as to whether critics should allow a new venture to "bed in" before they visit. In general, I think if punters are being charged full price, it's permissible to critique it. So I'll admit I'm breaking my own rule for Roganic – there's a 25 per cent discount during the first few services – but because of holidays, it's week one or not for ages. Too early? Well, the paint on the wall to the loos is still wet.

Roganic seats 25 in a single evening sitting, and to the left of me is a fellow newspaper critic, to the right a table of chefs checking out the competition, and opposite, a blogger snapping pictures of each dish, so that assuages any guilt I might have. That and the fact that Rogan's trusted chef Ben Spalding clearly needs to be cut slack by no one.

First, a box containing three different bread rolls each is put on the table. A ginormous pat of soft butter whipped with very posh salt is blobbed on to a stone for each of us. It feels a bit try-hard. But Jonathan Cannon and Sandia Chang are a front-of-house double act that manages friendly without faff and after a while it feels so convivial that I stop saying thank you and just beam as each plate is placed with care before me.

Rogan signatures are local, humble produce, unusual components and curious greenery. Certainly each of the 10 courses we eat has at least one "eh?" ingredient, be it ox-eye daisy petals (on a chickpea and lavender canapé), mallow (creamed and cubed, with a dainty crab and squid dish), chenopodiums (leaves wilted like spinach with earthy hogget) or cicely (an intense herbal plant to flavour ice-cream). Then there's the trickery: onion ashes, sourdough paper, chicken salt, strawberry glass. See what I mean about not being able to list everything?

One stand-out dish is Kentish seawater-cured mackerel with Regent's Park elderflower honey, broccoli – dehydrated and puréed – and shallots, which is a triumph of textures and flavours that plays on the tongue.

The other savoury stand-out is heritage potatoes with onion ashes, an ensemble imported from L'Enclume. OK, so the onion – baked, dehydrated then burnt – sounds like something from a parody of modern kitchen pretension, but my goodness it's divine.

Mr M is, by now, on to his third glass of Malbec, chosen on the advice of Zsolt Kismodi, the sommelier. I can see that not having a menu to hand might make it dicey ordering wine that accompanies food when you don't know what the food is, but Roganic's clientele strike me as the types to put themselves happily in the hands of the experts – or is that just me? The money I save by not having wine I splurge on a cheese course – the tray that arrives has 18 English and Irish varieties to choose from, all in very good condition. Then there are two puddings proper – brioche with smoked clotted cream and buckthorn curd, and the cicely ice-cream with strawberries and buttermilk – plus a shot glass of rich cherry nectar with home-made marshmallow.

The skill of the perfectly judged menu ensures that I feel sated but not stuffed. Roganic is not perfect, but for palates jaded by the procession of "it'll come when it's ready" tapas-style concepts and uncomfortably formal stellar cheffery (with waiting lists to match), it offers a delightful diversion.

9/10

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

Roganic 19 Blandford Street, London W1, tel: 020 7486 0380. Lunch and dinner, Tuesday to Saturday. £55 each for six courses, £80 for 10, plus drinks

Terrific tasting menus

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Seven Park Place

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A small and oddly split-up St James's dining-room, where William Drabble, formerly of Aubergine, is now chef, offering an excellent tasting menu.

Restaurant Nathan Outlaw

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Outlaw might change restaurants as most people do socks, but he is still one of the UK's top dozen chefs; his latest place has stunning views across the Camel estuary.

Reviews extracted from 'Harden's London and UK Restaurant Guides 2011' www.hardens.com