Spread mashed potatoes evenly in a buttered 13 x 9 baking pan. In a medium bowl mix together cheddar, bread crumbs, parmesan, paprika and pepper. Top mashed potatoes with cheese and bread crumb mixture and bake in the preheated oven for 10 minutes. After 10 minutes if the casserole is not brown on the top, turn on the broiler for a minute or two and remove from oven when browned. Allow to cool for 5 minutes and serve.