Roganic, 19 Blandford Street, London W1U 3DH

One of the questions I'm most often asked, when I tell people I review restaurants, is, 'Where have you been lately that's really special?'. And it's a difficult one to answer. The truth is, there aren't many places out there that really are that special. For every Fat Duck, there's a lot of ugly ducklings.

But now I have an answer to the question: Roganic. It's original, ambitious, artistic and rather bonkers. And it's certainly special.

It's the first London opening from Simon Rogan, the wildly inventive chef/proprietor of L'Enclume in the Lake District. If Heston Blumenthal is the king of avant-garde cooking in this country, Rogan is the prince in exile, with a fabled domain in Cartmel encompassing two restaurants, a hotel and an organic farm.

TV audiences got a glimpse of Rogan's style in The Trip, in which L'Enclume was the setting for Steve Coogan and Rob Brydon's exchange about foam. The good news about this new restaurant is that not only are there no foams in evidence, but it's geographically more central than L'Enclume, occupying a short-lease site in Marylebone.

They're calling it a pop-up, though with a potential life span of two years, it's more of a stay-up. The slender, storefront dining room has been tastefully refurbed on a shoestring, with Deco-ish pendant lights, turbulent black abstracts, and moss-green wainscoting which chimes with the foraged, herbivorous theme of the menu.

Never in the field of human dining have so many obscure herbs and sea vegetables laid down their lives in the service of a tasting menu. Chenopodiums and buckthorn, blite and Sweet Cicely – the menu should come with a copy of The Observer's Book of British Plants (not that Roganic offers anything as workaday as a printed menu).

We visited in the opening week, unsure of quite what to expect, but knowing, having visited L'Enclume, that it would be extraordinary. Certainly, the concept is bold. Not many new restaurants, in these straitened economic times, have the hubris to offer a no-choice set menu, at £55 for six courses, £80 for 10.

It's immediately apparent from the friendly welcome of the staff that though the prices might be high-end, the vibe of Roganic is refreshingly unstuffy. "How are you?" our waiter asked us. "How was your day? Been working?" (Yep, right now, I could have said, but didn't.) Some of the staff, along with the furniture and much of the produce, have come down from Cumbria, and their unceremonial directness is a breath of fresh air.

They're good at their jobs, too. Over a three-hour dinner, we were treated to a smooth flow of amazing, original dishes, largely vegetable-led, and garnished with herbs and flowers. The only familiar point came at the start of the meal, with some good, but conventional, bread served with butter whipped with Maldon salt and slathered onto pebbles.

After that, we were in uncharted waters. The combinations offered by Rogan and head chef Ben Spalding aren't just unlikely – they're downright odd. Roasted brill comes garnished with 'chicken salt': chicken skin rubbed with sea salt and thyme, like savoury popping candy. 'Vintage' potatoes are dusted with the ashes of dehydrated onions. The saltiness of seawater-cured mackerel is punctuated by droplets of warm elderflower honey, from nearby Regents Park. Goats' curd under an orb of beetroot jelly gets an aniseed bite from a hyssop purée – like a watercolour sketch of a conventional goats' cheese salad, only with the textures shimmeringly diffused.

It wasn't just the beauty of the dishes that made us keep reaching for metaphors from the visual arts. At their best, they provoke a synaesthetic reaction; a smoked egg yolk, slow cooked in a waterbath and partnered with sea vegetables and a warm breath of wild mustard sauce, stirred up some memory of eating smoky bacon crisps on a windy seaside cliff.

Pretentious as all this may sound, Roganic doesn't feel over-cerebral. I'm not generally a fan of cooking which involves tweezering microscopic ingredients onto weirdly-shaped plates, but here the flavour combinations really do repay the mind-boggling amount of labour that has gone into each dish. Even after three hours and 10-plus courses (plus, gulp, an optional selection of British cheeses) we felt stimulated, rather than overloaded.

Our fellow diners, in the opening week, were mainly foodie early-adopters, and Roganic will obviously appeal to the kind of gastronomic swingers who need to have their jaded palates teased. But it would be a shame if it didn't reach out to a wider clientele. This is the nearest I've come in Britain (outside the Fat Duck and L'Enclume) to the transporting theatricality of a meal at El Bulli. Passion, pride and some kind of obsessive craziness are at work here. So, all in all, pretty special, then.

Roganic, 19 Blandford Street, London W1U 3DH (020-7486 0380)

Food
Ambience
Service

Set menu: Lunch/dinner, 6 courses, £55; dinner, 10 courses, £80

Tipping policy: "Service charge is 12.5 per cent discretionary, of which 100 per cent goes to the staff; all tips go to the staff"

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