Stir sugar, butter and potatoes into eggs and beat until creamy.
Sift flour, baking powder, salt, nutmeg and cocoa together.
Alternately add milk and flour to egg mixture.
Chill well for 2+ hours (overnight even).
Roll 1/2 inch thick (*It is best to roll small amounts at a time and keep dough chilled as much as possible. Or you can roll, cut and return doughnut to fridge to keep chilled before frying. It makes it easier to handle).