Goat Cheese and Caramelized Onion Tarts

Cut thawed puff pastry into six 3- to 4-inch rounds using a cookie cutter. Roll edges of each pastry slightly to form 6 small tarts. Set aside.

Heat olive oil in a skillet over medium-high heat; stir in sweet onion. Cook and stir until onion has softened and turned translucent, about 5 minutes. Reduce heat to low and continue cooking and stirring until onion is very tender and dark brown, about 40 minutes more. Remove from heat and set aside.

Preheat the oven to 350 degrees F (175 degrees C).

Bring 1/3 cup balsamic vinegar to a boil in a saucepan. Reduce heat and let simmer until thickened, 5 to 10 minutes. Stir in 2 tablespoons balsamic vinegar and brown sugar. Remove from heat and set aside.

Divide cooked onions between the 6 tart shells and place on a baking sheet. Sprinkle goat cheese evenly on top of each tart.

Bake in the preheated oven for 7 minutes. Remove from the oven and drizzle each with balsamic vinegar reduction.

Return tarts to the oven and continue to bake until cheese is bubbly and tarts are golden brown, about 8 minutes more.