Preheat your oven to 400°F (200°C) and grease six 6-ounce ramekins with butter or cooking spray.

Roll out frozen puff pastry to about 1/8-inch thickness and cut out circles slightly larger than the tops of your ramekins.

Melt 2 tablespoons of unsalted butter in a medium skillet over medium heat and sauté the finely chopped onion until translucent, about 4 minutes.

Add minced garlic and mixed mushrooms, cooking for 8-10 minutes until mushrooms are golden brown and moisture has evaporated.

Sprinkle in 2 tablespoons of all-purpose flour and chopped fresh thyme, stirring to coat mushrooms and cook for an additional 2 minutes.

Gradually whisk in 1 cup of vegetable broth and cook until smooth and thickened, about 3-4 minutes.

Stir in 1/2 cup of heavy cream and let the filling simmer for an additional 5 minutes.

Season the filling with salt and pepper to taste, then divide among the prepared ramekins.

Sprinkle shredded Gruyère cheese over the filling in each ramekin, then place puff pastry rounds on top and gently press to seal.

Brush tops with a beaten egg and bake for 15-20 minutes until pastry is puffed and golden brown.

Remove from the oven and let them cool for about 10 minutes before serving.