Savory Caramelized Onion Tart

1.Preheat the oven to 400°F (200°C).

2.In a large skillet, melt the butter and olive oil over medium heat. Add the thinly sliced onions and cook, stirring occasionally, until they are soft and caramelized, about 20 minutes.

3.Sprinkle the sugar over the onions and continue to cook for another 5 minutes until the onions are golden brown. Stir in the balsamic vinegar and thyme leaves, then remove from heat and let cool slightly.

4.Roll out the puff pastry on a baking sheet. Using a sharp knife, score a border about 1 inch from the edge of the pastry. Prick the inside of the border with a fork.

5.Spread the caramelized onions evenly inside the border of the pastry. Sprinkle with the Gruyere and Parmesan cheeses. Season with black pepper to taste.

6.Bake in the preheated oven for 10-12 minutes, or until the pastry is golden brown and the cheese is melted and bubbly.

7.Garnish with chopped fresh parsley before serving. Cut into slices and enjoy!