In a large mixing bowl, combine 2 cups flour, sugar, yeast and salt. In a saucepan, heat milk, shortening and water to 120 degrees F-130 degrees F. Add to dry ingredients; beat until moistened. Add mashed potatoes and eggs; beat until smooth. Stir in enough remaining flour to form a stiff dough. Do not knead. Place in a greased bowl, turning once to grease top. Cover and refrigerate for several hours or overnight.