You have to push your way through a packed tapas scene in the bar to get to the stairs down to an underground warren of tiled rooms. The cuisine of “The Nest” is Asturian, a regional favorite with Madrileños, and it’s reflected in the fish-intensive menu, including the Asturian classic of hake braised in cider. You don’t have to be a fish-lover to eat Asturian, though. El Ñeru makes a hearty fabada Asturiana of large white beans stewed with ham and sausage, and, for the more adventurous, a stew of tripe and garbanzo beans. A Madrid friend swears that the restaurant also makes the city’s best arroz con leche, a creamy rice pudding with a caramelized top. Bread service includes a great spread of butter blended with Cabrales blue cheese, and the meal ends with a thimble of a yellow-green digestive liqueur.