1 tablespoon olive oil
1 large yellow onion, chopped
1 tablespoon unsalted butter
16 ounces white button mushrooms, chopped
1 clove garlic, chopped
½ teaspoon dried thyme
Salt and pepper, to taste
¼ cup white wine
1 package of puff pastry shells
1 cup shredded Swiss Cheese (I used some tasty amish swiss)
1 egg + 1 tablespoon water, beaten together (for the egg wash)
While your oven is preheating, take your pastry shells out of the box and place them on the cookie sheet. Lightly brush them with the egg wash. Once the oven is ready, bake them for about 15 minutes so they rise up and get slightly golden.
While those are baking, heat the olive oil in a wide, heavy-bottomed pan over medium-low heat and add the onions. Cook, stirring occasionally, until they begin to caramelize. Depending on your pan, it can take 10 - 20 minutes.
Add the garlic and the thyme and saute until fragrant, about 1 minute. Season with salt and pepper to taste.
Add the wine, scraping the bottom of the pan to pull up all of the browned bits, and cook until all of the liquid has evaporated. Remove from heat.
Fill it up with your mushroom and onion filling.
Top it off with some of the shredded swiss.
Then put back in the oven and bake for another 5 - 10 minutes.