2 prepared pizza crust, unbaked (either storebought or your own recipe)
3 cups mashed potatoes (either leftover or reconstituted instant mashed potatoes are fine)
1 large onion, peeled and diced
12 cup butter or 12 cup margarine
8 ounces cheddar cheese, grated
8 ounces provolone cheese, grated
8 ounces mozzarella cheese, grated (mix with provolone cheese)
Saute onion in butter or margarine until translucent and golden; stir into mashed potatoes along with cheddar cheese. Refrigerate to let flavors meld. Preheat oven to 400F. Spread pizza crusts with potato mixture. Top with Provolone and Mozzarella cheese mixture and bake until shells are baked and cheese is melted.