- 2 cups very thinly sliced onion (about 2 onions)
- 1 1/2 tablespoons unsalted butter
- 2 tablespoons water
- 3/8 teaspoon salt
- 1/8 teaspoon black pepper
- 1 (9-inch) refrigerated pie shell (from a 15-ounce package)
- 3 tablespoons crème fraîche at room temperature
- 1 1/2 teaspoons finely chopped fresh chives
- Special equipment: a 2 1/4-inch round cookie cutter; a mini-muffin pan with 12 (1/8-cup) muffin cups
- Put oven rack in middle position and preheat oven to 375°F.
- Cook onion, butter, water, salt, and pepper, covered, in a 10-inch heavy skillet over moderately low heat, 10 minutes. Remove lid and cook, stirring frequently, until onion is deep golden brown and very tender, about 25 minutes.
- While onion cooks, roll out dough to slightly less than 1/8 inch thick. Cut out 12 rounds with cutter and lightly press each into a mini-muffin cup. Bake until pale golden, 10 to 12 minutes. Remove tartlet shells from muffin pan.
- Stir together crème fraîche and chives and divide among shells, then top with caramelized onions.