Peel potatoes; boil until tender. Mash; cool. Add egg, salt, cheese, flour and nutmeg; mix well. Knead lightly until smooth. Shape into long thick roll; cut into 3 cm pieces. Roll into dumplings. Cook in rapidly boiling salted water until dumplings rise to surface; simmer for 5 to 7 minutes longer or until cooked through. Drain; pour butter over dumplings.