Grate the cooked and cooled potatoes very finely on a kitchen grater. Mix in a bowl with the salt and egg yolks. Then stir in the softened butter until a smooth paste has formed. Then the buttermilk is stirred in. Mix the flour with the baking powder and baking soda and stir in as well. Beat the egg whites until stiff and fold in with a spatula.
Bake the dough bit by bit in the preheated waffle iron according to the manufacturer`s instructions. It may be that you also need butter, I don`t need any for my waffle iron.
The waffles are delicious, still warm, for breakfast with a slice of fried bacon and eggs. Or as an accompaniment to soup and other dishes.