Mushroom Thyme Bites

Directions

1. In a large skillet over medium high heat, melt butter with oil. Add the mushrooms and sauté for about 5 minutes until tender. Remove and set aside in a medium bowl.
2. In the same skillet over medium high heat, cook the onion until softened, about 5 minutes. Add the garlic, thyme, brown sugar, salt and pepper and continue to cook for 25 minutes on medium low heat, stirring occasionally. Add the broth to deglaze the pan, allowing the onions to soak it all in. Add the onions to the mushroom mixture, stirring to combine. Allow to cool to room temperature. Stir the Gruyere cheese to combine.
3. Position two racks in the upper and lower thirds of the oven. Preheat the oven to 400°F (200°C). Line 2 baking sheets with parchment.
4. Using a knife or a pizza cutter, cut the puff pastry into 2-inch (5cm) squares and place them on a lined baking sheet. 
5. In small bowl, whisk together yolk with water. Using a pastry brush, brush the egg mixture over the squares. Place a scant tablespoon of caramelized onion mixture in the center. Bake for 10 - 12 minutes, until crisp and golden brown. Let cool slightly before serving.