- Preheat oven to 400F. Heat butter in saute pan, saute leeks, garlic, mushrooms until tender.
- Add salt, pepper, dried thyme, parmesan, and cream. Bring to boil then reduce until thick. Remove from heat and cool.
- Unfold puff pastry into a large square. Pour mushroom mixture over tart leaving a crust.
- Bake at 400 degrees until pastry is brown, about 10-12 minutes.