A VISIT TO this perpetually bustling, standing room-only tapas bar is an education.It is a study first in how an inspired, smart design team (Partisans) and a good batch of African mahogany can transform an ordinary-looking little watering hole (Teatro) into a place of transporting beauty. Then, there’s the pintxos and tapas. Amid the former, the tuna pickle gilda is a perfect way to begin. So is the morcilla (blood sausage) if you fancy something more robust. Then, for your second lesson, turn to the canned seafood. If you think fresh seafood is better than tinned, think again. There is a time for each. In Spain, where the fish markets are immeasurably better than our own, many a discriminating consumer still values the tinned goods over the fresh (a small can of top-quality, olive oil-packed squid, cockles, octopus or baby eels can easily set you back $50). You can spend that here, too, on an imported can of some cockles or white clams (both lovely).But be advised that one of the very best tinned offerings is produced in-house, sold at modest cost and is one of the most pleasing in the entire selection: firm, luscious, bite-sized pieces of smoked mackerel. Naturally, there is also quality jamón ibérico, correctly hand-sliced. And the hot sharing plates include such pleasures as a snail and mushroom sauté and some tip-top croquetas. At lunch, food is fanned over the bar, and you can have a look and take what you like: a ham sandwich in a croissant, say, followed by a wedge of Basque cheesecake, maybe two. The cocktails are excellent, and the list of sherries is pleasingly extensive. The wine list is short, but the Spanish offerings are well-curated.