Mix the mashed potatoes, shortening, sugar, salt, and flour. Knead until you have a good dough. Cut into sections, roll out thin and cook on a greased (if needed) griddle until light brown, turning frequently to avoid scorching. After cooking each one, place them between a hand towel, to keep them from drying out. When cool, place in ziplock bags with the towels. To store them place the bags in the refrigerator (5 days) or freezer (six months). Serve with butter and sugar. Brown sugar is my favorite!