In a mixing bowl put warm mashed potatoes, shortening, sugar and salt. Beat to a cream and add 2 eggs, the yeast cake dissolved in cup of lukewarm water. Use about 2 cups of the flour to make a thin batter. Cover and let it raise over night. When well risen add 4 cups of flour to make as stiff a dough as can be stirred well with a mixing spoon. Roll out dough to 1/2 inch thickness on a floured board. Cut into squares about the size of a soda cracker. Bring each of the 4 corners, of each square, to the center and pinch together. Place a small piece of butter on top of each. Put on greased baking sheets about 2 inches apart and stand in warm place to rise until very light. Bake in hot oven (400F) for 15 to 20 minutes. While still hot, brush with melted butter and dust with powdered sugar or sugar and cinnamon mixed.