1. Wash, peel, and cut the mushrooms into pieces.
2. Sauté them in a pan with a little oil for about ten minutes.
3. Off the heat, add the cheese, cream, salt, and pepper. Mix well.
4. On a baking sheet or in a pie dish, roll out one puff pastry and pour the mixture in the center. Cover with the other puff pastry and seal by rolling the edges properly.
5. Beat the egg yolk and brush it over the pie using a brush.
6. Bake in a preheated oven for 10 minutes at 180°C (350°F), Gas Mark 4, then let it cook for about 30 minutes.
7. Enjoy your meal!