Heat 2 tablespoons of olive oil and 1 tablespoon of butter over medium heat in a large skillet. Add 2 sliced onions, 1 teaspoon of sugar, and a pinch of salt and pepper. Cook for about 15 minutes, stirring occasionally, until onions are caramelized.

Stir in 1 tablespoon of balsamic vinegar and a few sprigs of fresh thyme to the caramelized onions. Cook for another 5 minutes until the mixture is jammy and glossy.

Roll out a sheet of puff pastry on a floured surface and cut into rectangles about 3x4 inches. Place on a lined baking sheet.

Distribute the caramelized onion mixture onto the pastry rectangles and crumble goat cheese on top. Add more fresh thyme if desired.

Preheat oven to 400°F (200°C) and bake for 15 minutes or until golden brown.

Let cool for a few minutes before serving warm.