Soak the stockfish for 24 hours, dry them, and stew them in a little water on a low flame. Get rid of skin and bones. Turn the fish meat through the meat grinder.
Boil and puree the potatoes. Knead the fish meat with the same amount of mashed potatoes and very finely chopped onion browned in butter. Add some milk if necessary. Season to taste with salt, pepper and butter, chill.
Form small croquettes with two spoons and roll them in breadcrumbs, beaten egg and again in breadcrumbs until they are well covered. Fry in very hot oil. Serve hot or cold.