Sift together dry ingredients and rub cold butter into the flour with your fingers until it resembles a coarse meal. Add the mashed potatoes and mix with a fork. Make a well in the center and pour in milk. Incorporate the flour into the milk until you can form a ball adding additional milk if needed.
On a floured surface turn out dough and knead until you have a smooth dough. Roll out into a circle about 1/4 inch thick. Cut into triangles. Heat a cast iron pan with a dab of melted butter over medium heat. Careful not to burn the butter. Fry the scones about 3 min. a side until golden brown. Serve hot with a dab of butter.