Line deep 8-inch pie plate or spring pan with pastry.
Heat butter in skillet, add onions and bacon; fry 3-4 minutes. Beat eggs in a bowl. Add warmed milk, drained onion and bacon, salt, pepper, mustard and parsley. Pour into pastry shell.
Cook in 375 degree oven for 35-40 minutes. If desired, garnish with extra slices or broiled bacon. Makes 6 servings.