Steps
1. Preheat the oven to 200°C (390°F).
2. Heat olive oil in a pan over medium heat. Add the sliced onions and cook slowly, stirring occasionally until they become golden and caramelized (about 15-20 minutes).
3. Add the balsamic vinegar, thyme, salt, and pepper; cook for another 2 minutes. Remove from heat.
4. Roll out the puff pastry on a baking sheet lined with parchment paper.
5. Spread the caramelized onions evenly over the pastry, leaving a small border around the edges.
6. Crumble goat cheese over the onions.
7. Fold the edges of the pastry slightly inward to create a crust.
8. Bake in the oven for 15-20 minutes until the pastry is golden and puffed.
9. Remove from oven, let cool slightly, and serve warm.