Grate the potatoes on the large holes of a hand grater or in a food processor; grate the onions more finely. Combine the potatoes and onions in a colander and drain well, pressing out as much moisture as possible. Beat the eggs in a large bowl, then add the flour, salt, baking powder and pepper. Mix until smooth and then stir in potatoes and onions. Heat about 1/8-inch of oil in a large cast iron skillet, or griddle until hot; a drop of batter should sizzle. Drop the pancake batter by large spoonfuls and spread each into a thin pancake. Fry until bottom is brown and crisp, then turn and cook until the second side is also brown and crisp. Drain on paper towels and keep warm in a 200°F oven until all the pancakes are done. Serve with sour cream and applesauce.