Beat mashed potatoes to a soft cream with milk, salt, pepper, and mix in a little melted butter - a small tablespoonful for each cupful of potato. Whip in the beaten yolks of two eggs and at the last the frosted whites. Have a little hot butter in a frying-pan, pour in the mixture and cook slowly until it is well set. Ten minutes should suffice. Double and turn out upon a hot dish.