In a large bowl, combine sugar and mashed potatoes. Add water and yeast; mix well. Cover and let rise in a warm place for 1 hour.
Meanwhile, combine filling ingredients and set aside. Stir dough down; beat in the butter, eggs and salt. Gradually stir in flour. Turn out onto a lightly floured surface; knead until smooth and elastic, about 6-8 minutes.
Divide dough in half. On a floured surface, roll each portion into a 12-in. square. Spread filling to within 1 in. of the edges of each square. Roll up jelly-roll style. Cut each roll into nine slices. Arrange nine rolls in each of two greased 9-in. square baking pans. Cover and let rise in a warm place until doubled, about 1 hour.
Bake at 350° for 35-40 minutes or until golden brown. Drizzle with icing if desired.