Boil the sweet potatoes for 20 to 30 minutes or until tender. Drain & peel while still warm. Mash. Mix in all the remaining ingredients except the ghee. Knead till thoroughly blended. Divide into 8 portions. Wash & dry hands & then rub with oil. Roll each ball in your hands & then flatten into a patty. Brush with ghee a griddle or skillet. Over the lowest heat possible, heat the ghee & then fry the patties for 15 to 20 minutes each side until a crisp reddish brown crust forms. Serve hot. Yamuna Devi, "The Art of Indian Vegetarian Cooking"