Caramelized Onion Tartlets

On a lightly floured work surface, roll pate brisee to 1/8-inch thickness. Using a 2-inch-round biscuit cutter, cut out 12 circles. Transfer to a parchment-lined baking sheet, and refrigerate until needed.

Melt butter in a heavy-bottomed skillet over medium heat. Sprinkle sugar over butter; cook, stirring, until sugar melts and starts to turn amber in color.

Halve onions crosswise. Season cut surface with salt and pepper. Arrange onions in a single layer, cut side down, in skillet. Cook over medium-low heat, without turning, until caramelized sugar bubbles up around onions and onions are fragrant, about 15 minutes. Remove from heat.

Using a slotted spoon or spatula to keep onions intact, transfer them to mini-muffin tins, placing half an onion, cut side down, in each cup (allow sugar syrup to remain in pan). Return skillet to low heat. Stir in balsamic vinegar, and season with salt and pepper and a few leaves of fresh thyme.

Heat oven to 425 degrees. Quickly, before sugar cools, spoon a generous teaspoon sugar mixture into each muffin tin. Drape chilled pastry rounds over each onion, and using fingers, press to secure. Onions should be swaddled in pastry. Place muffin tin in oven; bake until pastry is golden brown and sugar bubbles up over pastry, about 20 minutes. Remove from oven. Immediately set baking sheet over muffin tin; invert, being careful of hot caramel that might drip from tin. Once you invert the tins, tarts will be right side up; serve garnished with fresh thyme leaves.