Swiss Onion Quiche

1-9” deep dish pie shell, unbaked
2 tsp butter
¾ cup chopped onion
1-½ cups shredded Swiss cheeses
3 eggs
1-½ cups half-and-half
½ tsp salt
1/8 tsp cayenne pepper
*Heat oven to 425˚. In skillet, melt butter. Cook and stir onions 5 minutes or until tender. Spoon into pie shell. Sprinkle with cheese. Beat eggs slightly. Beat in remaining ingredients. Pour into pie shell. Bake 15 minutes. Reduce oven temperature to 325˚. Bake 30 minutes longer or until knife inserted into center comes out clean. Let stand 10 minutes before cutting.
(May add ½ cup chopped ham or cooked bacon with the onions.)