If you dine on the sidewalk terrace at this tony end of Calle Jorge Juan, you’d never suspect that the main dining rooms downstairs have stone walls and the dark, homey feel of a Basque tavern. This family-run establishment opened nearly a half century ago to bring Basque cuisine to its homesick countrymen. Over time, the cooking has become more modern and sophisticated without deviating from the tried-and-true formula of buying the best available products and being careful not to mess them up. There are some Basque classics that need no updating, including the sopa de txanguerro (spider crab soup), bacalao a pil pil (cod in an emulsification of olive oil and fish juice), and turbot in garlic sauce.