- Cook puff pastry shells as directed.
- Finely dice mushrooms and onions, and sauté in butter until browned and all the liquid has evaporated.
- Transfer to a bowl and while still warm, blend in cream cheese or goat cheese and mustard. Mix well.
- Add salt and pepper to taste.
- Remove tops for pre-baked pastry shells and fill with mushroom mixture.
- Bake at 350 degrees F. for 10-15 minutes until heated through.
- Remove from oven, replace tops and serve hot.