In a large bowl, sift together the flour, mashed potato, baking powder, salt and sugar. Make a well in the center and pour in the milk, egg and melted butter and farmers cheese if using; mix until smooth. Heat a lightly buttered griddle or frying pan over medium high heat. Pour or scoop the batter onto the griddle, using approximately 1/4 cup for each pancake. Brown on both sides and serve hot with maple syrup.