Gruyere Mushroom and Caramelized Onion Tart

4 tablespoons butter

2 tablespoons vegetable oil

140 grams mushrooms, sliced

2 medium yellow onions, sliced

1/4 teaspoon dried thyme

1 tablespoon sugar

1-1/2 tablespoon balsamic vinegar

1/4 teaspoon garlic powder

salt and pepper, to taste

140 grams grated gruyere cheese

1 package puff pastry

1 egg, lightly beaten

In a large skillet over medium heat, heat 1 tablespoon of oil along with 1 tablespoon of butter. Add the mushrooms and sauté for about 5 minutes until tender. Remove and set aside in a bowl.

Heat the remaining 3 tablespoons of butter along with the 1 tablespoon of oil and sauté the onions for 5 minutes. Add the dried thyme and sugar and continue to cook for 25 minutes on medium low heat. Make sure to stir the mixture every 5 minutes or so. Add the balsamic vinegar to deglaze the pan, cook until the mixture dries out. Add the mushrooms. Season with the garlic powder and salt and pepper to taste. Allow to cool to room temperature. Add the gruyere cheese and mix well.

Preheat the oven to 220 degrees C. Line 2 baking sheets with parchment paper. Cut the puff pastry into 5 cm squares and place them on a lined baking sheet. Make sure the puff pastry is cold before proceeding. Using a pastry brush, brush the beaten egg on the squares. Place a tablespoon of caramelized onion mixture in the center. Bake for 20-25 minutes, until crisp and golden brown. Let cool slightly before serving.