1. Place pie pastry in pie dish. Fill pie with bacon, cheeses and mushrooms.
2. In medium bowl mix together eggs, salt, onion, whipping cream, sugar, and cayenne pepper. Pour egg mixture over pie.
3. Bake at 425 degrees F for 15 minutes. Reduce oven temperature to 300 degrees F. Bake an additional 45 mins or so, til a knife can be inserted 1 inch away from sides comes out clean. Let stand 10 minutes.