Preheat a broiler. Place the unpeeled onions in a small baklng pan and cover with aluminum foil.

Place in the broiler about 5 inches heat source and broil (, turning every 5 to 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 ¾ inch 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 l!ghtly browned and fragrant, 2 to 3 minutes. Transfer the seeds to a cutting board and crush with the flat side of a knife. 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. Taste and adjust seasoning. 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.