Making Elegant Mushroom Goat Cheese Tarts can be straightforward if you follow these steps closely:

1. Preheat Oven: Begin by preheating your oven to 400°F (200°C). This will ensure the pastry bakes evenly and achieves that perfect golden brown color.

2. Prepare Puff Pastry: Roll out the thawed puff pastry on a lightly floured surface to about 1/8 inch thick. Cut into squares or circles, depending on your tart molds.

3. Sauté Mushrooms: In a skillet over medium heat, add olive oil. When hot, add the diced onions and cook until translucent. Add the minced garlic, stirring until fragrant. Then add chopped mushrooms, season with salt and pepper, and sauté until they release moisture and become tender, about 5-7 minutes.

4. Mix Filling: In a bowl, combine the sautéed mushroom mixture, softened goat cheese, and thyme. Stir until combined and taste to adjust seasoning if needed.

5. Fill Pastry: Place the pastry squares or circles into your tart mold or on a baking sheet lined with parchment paper. Fill each pastry with a spoonful of the mushroom and cheese mixture.

6. Add Egg Wash: Beat the egg in a small bowl. Brush the edges of the pastry with the egg wash for a golden finish.

7. Bake Tarts: Place the tarts in the preheated oven and bake for 20-25 minutes or until the pastry is puffed and golden brown.

8. Cool Slightly: Once baked, remove the tarts from the oven and allow them to cool for a few minutes. This will make handling easier and will help the filling set a little.

9. Garnish (Optional): If desired, sprinkle fresh parsley or chives over the tarts for added color and flavor before serving.

With these steps, you will create a batch of amazing Elegant Mushroom Goat Cheese Tarts that are sure to impress you and your guests.