Preheat oven to 375°. For the crust, combine butter cracker crumbs and melted butter. Press into bottom and up sides of a 10-inch pie pan. Fry bacon and chopped onion together until bacon is browned and onion is softened. Drain. In mixing bowl, combine bacon and onion, eggs ,sour cream, cream cheese, Swiss cheese, salt and pepper. Mix well. Pour into prepared cracker crust. Top with 1/2 cup grated Cheddar cheese. Bake for 20-30 minutes until knife inserted into center comes out clean. Let stand 5-10 minutes before cutting.