Peel potatoes and boil in salted water until tender. Drain. While still hot, rice the potatoes. Measure out 4 cups slightly packed into mixing bowl along with butter and salt. Stir well. Dont add sugar until cool or it will make the dough watery. Chill well in refrigerator. Prepare up to this point the night before. Cut in the flour and sugar then blend in cream. Turn out, knead briefly, divide in half and shape into two logs. Cut each log into 12 equal pieces. Put half back in fridge to keep cool. Heat griddle to 400 degrees. With stocking covered rolling pin, roll to 1/8 inch thick or less (thinner the better) adding plenty of flour as you roll. Cook on griddle until lefsa starts to bubble and golden spots appear. Pop bubbles. Roll next Lefsa while cooking. Turn and cook other side. Cool under folded towel so they dont dry out. Make 2 stacks, alternating to keep from getting soggy. Refrigerate. To freeze, stack with wax paper between. Put in ziplocks or Foodsaver vacuum bags.