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

Roll out chilled puff pastry on a floured surface to about 1/8-inch thickness, and cut circles larger than the tops of ramekins.

Melt 2 tablespoons of unsalted butter in a skillet over medium heat. Sauté the diced onion for about 4 minutes until translucent, then add minced garlic and cook for 30 seconds.

Stir in the mixed mushrooms and cook for 8-10 minutes until golden brown.

Sprinkle 2 tablespoons of flour over the mixture and cook for 2 minutes while stirring constantly.

Gradually add 1 cup of vegetable broth, stirring continuously until the mixture thickens after 3-4 minutes.

Stir in 1/2 cup of heavy cream and simmer for about 5 minutes, then season with salt and black pepper.

Evenly divide the filling among prepared ramekins and top with shredded Gruyère cheese.

Cover with puff pastry circles, crimping edges to seal. Brush tops with beaten egg.

Bake for 15-20 minutes until golden brown.

Let pot pies cool for about 10 minutes before serving.