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It'll never match a night out in San Sebastián, but it's a damned fine try
Walking towards Donostia, we pass a pair of natty, pointed men's shoes at an artful angle outside a Marylebone boutique. It looks as though a dapper, window-shopping elf has spontaneously-combusted. Nearly as curious is the fact that a Serbian chap, an English gal and a Polish chef have opened a restaurant specialising in the cuisine of San Sebastián – aka Donostia.
San Sebastián is the heaven that I want to die and go to. It's the foodie equivalent of sex tourism – a place to indulge unjudged. The city has a few Michelin-starred big hitters, but the hardcore sensationalist is here for the txikiteo, or bar crawl. The locals have a snifter and a pintxo in each; foreigners eat themselves into seven kinds of oblivion. Because they can. The difference between this and a carnival of all-you-can-eat buffets is that everything you try – every beef cheek, every sliver of Ibérico, every plancha'd wild mushroom – will be ambrosial.
Of course, it's not just Donostia's parentage that isn't Donostian, but the fact that you're here for actual dinner. In San Sebastián, you'd have tortilla in Nestor, an anchovy or two in Txepetxa and wild mushrooms in Gambara. So we attempt to recreate a txikiteo in the one restaurant, by eating everything on the menu apart from deep-fried prawns with mango that sound a bit Berni Inn, and by drinking tourist quantities of wines, from young txacoli, poured from a height into wide tumblers to give it extra "life", to godello, described accurately as having notes of peach, anise and ripe apple (owners Nemanja Borjanovic and Melody Adams are wine importers). There's Basque cider, too. It appears from the bill that we have quite a few corkers, but details are a little, um, hazy.
There's some top stuff here. Meat is a particular strength. Pluma, that lusciously-marbled cut of Iberian pig here described as "shoulder" (it's a bit more complicated than that) is lustworthy: smoky crust, juicy, rosy-pink centre, with a romesco of roast peppers and almonds. Lamb chops are equally good, chomped like lollipops from their charred wee bones; and steak is from O'Shea's, which is as good as having "bloody gorgeous" branded on to its flank.
You can book a table, but the little open kitchen fringed with stools is for walk-ins, so you can watch the ham-carving, frying and emulsion-whisking. A special of a blowsy courgette flower, its petals swollen with creamy goat's cheese, is fried until lacy and crisp. Croquetas – as good a benchmark for a Spanish restaurant as the equally deceptively simple carbonara is for an Italian one – are sexy little balls generously studded with jamón, or with prawns in a shellfish béchamel that's as pungent as lobster bisque.
Tortilla is identical to the one at Barrafina, where chef Tomasz Baranski worked before, and is a miracle of engineering: its outside firm and fluffy, its innards sticky with caramelised onion and oozing.
Maybe they're equally ace at fish? Cod cheeks pil-pil deliver slithery little dollops in a chilli-kissed sauce, an emulsification of olive oil and the fish's juices. It's better than many I've had in the homeland: less challengingly gelatinous. Deep-fried txipirones, the weeniest baby squid, are pleasingly crunchy and greasy: the ultimate bar snack. And there's a miraculous rendition of cuttlefish on arroz nero: the cephalopod as tender as marshmallow, the inky rice wonderfully intense. Servings are typically small, and overindulgence can see bills mount from mild ouch to actual physical pain.
Baranski has worked at two San Sebastián restaurants, the trad Urepel and the more rock'n'roll, wagyu burger-toting A Fuego Negro. Perhaps in "Portman Village" you might not be able to stagger from one great bar to the next (although Vinoteca over the road is pretty hot stuff), but given that everyone tries to ape the utopian ideal, Donostia may not be the head-scratcher it first seemed. The mystery of those shoes, however, remains.
• Donostia, 10 Seymour Place, London W1, 020-3620 1845. Open lunch, Wed-Sat, noon-3pm; dinner, Tues-Sat, 6-10.30pm. Meal with drinks and service, around £50 a head.
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• This article was edited on 10 September 2012. In the original, we misidentified Nemanja Borjanovic as Siberian. This has been corrected.