PLACE SWEET POTATOES in a mixing bowl, add egg and mix well. Stir in the flour and add the baking powder. Add up to 1/3 cup of milk, stirring. Stir in 1 tablespoon butter. The mixture should have the consistency of thick, lumpy sauce and be able to coat a wooden spoon. Place a non-stick or heavy iron skillet over medium heat on top of the stove and add 1/2 teaspoon butter. Spoon 3 tablespoons of batter per pancake into the skillet and cook until bubbles rise to the surface of the pancakes and break, about 1 to 2 minutes. Using a spatula, flip the pancakes and cook another 2 minutes. Remove pancakes from the skillet and keep warm on a covered plate in the oven. Repeat the procedure until all the pancakes are cooked. After the first batch is cooked, add as little butter as possible without allowing the pancakes to stick to the bottom of the pan. Serve with sour cream. Makes 12 small pancakes.