Potato Puff
["2 c. mashed potatoes", "1 Tbsp. butter", "1 egg, separated", "1 tsp. chopped parsley, optional", "Grated cheese"]
["Blend potatoes with egg yolk and butter.", "Beat until light and creamy.", "Add parsley and cheese; fold in stiffly beaten egg white.", "Place in buttered 1-quart baking dish.", "Sprinkle with cheese.", "Bake at 350 degrees for 30 minutes.", "Makes 4 servings."]
["potatoes", "butter", "egg", "parsley", "cheese"]