Put the whole, unpeeled potatoes in a pot and cover with cold water by 2 inches. Bring to a boil and simmer gently until a fork goes through the potatoes with little resistance, about 40 minutes.
Cut the potatoes into smaller chunks and press through a ricer. If you don't have a ricer, peel the potatoes and mash with a fork or masher. Measure out 4 loosely-packed cups of riced potatoes and put in a large bowl. Heat the heavy cream, butter, sugar and salt in a small pot until the butter melts. Add the butter/cream mixture to the potatoes and mix gently. Put the mashed potatoes in the refrigerator to cool down, about 30 minutes. Once cooled completely, add the flour and work it gently into the potatoes. Do not over work the dough. Allow to rest at room temperature for 10 minutes.
Take 2 tablespoons of dough and form it into a ball. Sprinkle flour on a sheet of parchment or wax paper. Using a rolling pin, roll out the dough into a very thin circle, about 1/16-inch thick and 7 inches wide. Flour the dough as necessary to avoid sticking.
Heat a large nonstick skillet over medium heat. Turn the parchment or wax paper upside down and gently peel off the thin circle of dough onto your hand. Place the dough directly in the heated skillet. Cook on one side until some brown speckles start to form, about 1 minute, and then flip the dough and cook for an additional 30 seconds. Transfer the cooked lefse to a plate and keep covered with a clean kitchen towel. Repeat with the remaining dough.
To serve, spread butter and sprinkle sugar on a warm lefse and roll it up. If the lefse is cold, you can warm it up quickly in a heated skillet.