Mix butter into flour; add good pinch of salt. Mix in mashed potato; pour in milk to make soft dough. Roll out on lightly floured surface; cut into rounds 8 cm across. Put on greased baking sheet; bake at 220ºC or 15 to 20 minutes. Split; serve hot with butter. Preparation time: 15 minutes Baking time: 15 to 20 minutes