Potato Puff Casserole
["4 c. mashed potatoes", "1 c. shredded Cheddar cheese", "4 egg yolks", "2 tsp. chopped onion", "2 tsp. finely chopped green pepper", "1/2 tsp. celery salt", "4 egg whites", "salt and pepper to taste"]
["Beat mashed potatoes, salt, pepper and egg yolks together. Add celery salt, cheese, onion and green pepper.", "Beat egg whites to soft peaks; fold into potato mixture.", "Spoon lightly into a greased 7 x 13-inch baking dish.", "Bake for 25 minutes at 375\u00b0."]
["potatoes", "Cheddar cheese", "egg yolks", "onion", "green pepper", "celery salt", "egg whites", "salt"]