1 ready made 9" pie shell
1 3/4 c. grated Swiss cheese
1 med. onion
1/2 lb. mushrooms
4 eggs
1 1/2 c. milk
3 tbsp. flour
1/4 tsp. salt
1/4 tsp. dry mustard

Cover bottom of pie shell with grated cheese. Chop onion and mushrooms; saute in butter, salt and pepper. Pour mixture over cheese.

Make a custard by beating together eggs, milk, flour, salt and dry mustard. Pour custard over mushroom layer. Bake at 375 degrees for 40-45 minutes or until solid in the center when jiggled.