Line a 9-in. deep-dish pie plate with pastry. Trim to 1/2 in. beyond edge of plate; flute edges. Line pastry shell with a double thickness of heavy-duty foil. Bake at 400° for 5 minutes. Remove foil; bake 5 minutes longer.
In a small skillet, cook sausage over medium heat until no longer pink; drain. Spoon sausage into crust; sprinkle with cheese. In a small bowl, whisk the eggs, cream, mushrooms, peppers and onion; pour over cheese.
Bake at 375° for 40-45 minutes or until a knife inserted in the center comes out clean. Let stand for 10 minutes before cutting.