Some of Spain's most amazing restaurants focus on one ingredient. Here, three obsessions.

Ham In Seville's old Triana quarter, Jaylu serves the best ham in Spain. The owner is adept at carving jamón into slices of various thicknesses, creating textures that range from rustic to ephemeral. DETAILS López de Gomara 19; 011-34-954-339-476.

Mushrooms Cisne Azul, off Madrid's trendy Chueca Square, specializes in seasonal wild mushrooms. Whether they're chanterelles or rarer local varieties, the preparation is the same—a quick sauté in olive oil—and they're incredible. DETAILS Gravina 19; 011-34-915-213-799.

Roast Lamb Lechazo—suckling lamb roasted whole in a wood oven and served with only its own juices—is something of a religion in parts of Castilla. One pilgrimage-worthy restaurant: Asador El Cípres, in Aranda del Duero. DETAILS Plaza Primo de Rivera 1; 011-34-947-507-414.