4 medium-large yellow sweet onions, unpeeled 1 tablespoon cumin seeds 1/2 cup (2 oz/60 g) grated asadero, Manchego, Monterey Jack or other good melting cheese 1 cup (4 oz/125 g) grated Cotija, Romano or other aged cheese 3 tablespoons sour cream 1 tablespoon balsamic vinegar 3 dashes of hot-pepper sauce such as Tabasco 1/2 teaspoon salt 1/2 teaspoon freshly ground pepper
Preheat a broiler (griller). Place the unpeeled onions in a small baking pan and cover with aluminum foil. Place in the broiler about 5 inches (13 cm) from the heat source and broil (grill), turning every 5-10 minutes, until charred on the outside and soft all the way through, about 1 hour. Remove from the broiler and set aside to cool. Set the oven temperature to 375°F (190°C). Peel the onions carefully, keeping them intact and discarding the outer charred skin. Cut the onions in half crosswise and, using a finger, remove the centers, forming roasted onion "cups" with walls about 3/4 inch (2 cm) thick; reserve the centers. Line the bottom of each onion cup with a piece of the removed roasted onion to prevent the filling from leaking out. In a small frying pan over medium heat, toast the cumin seeds, shaking the pan frequently, until lightly browned and fragrant, 2-3 minutes. Transfer the seeds to a cutting board and chop coarsely. Chop the remaining removed onion pulp and place in a small bowl. Add both cheeses, sour cream, cumin seeds, vinegar, hot-pepper sauce, salt and pepper and stir to mix well. Divide the cheese mixture evenly among the onion cups. Place on a baking sheet and bake until browned and bubbling, 15-20 minutes. Serve hot.
