1. Wash potatoes and peel them, then drop them into cold water. Let stand 1 or 2 hours or overnight, if desired. Grate the potatoes with a fine grater and press the potatoes to squeeze out excess liquid.
2. Peel and grate the onion into the potatoes and add the egg, seasonings and soda. Mix well.
3. Heat butter in a large skillet and add one spoonful of the mixture for each pancake. They should not be too thick. Cook gently until golden brown on the bottom, turn and brown the other side. Add more butter to the skillet and continue cooking the pancakes in this fashion until all the mixture is used.