Cook potatoes in boiling water until tender, about 20 minutes. Drain and rinse potatoes, then pat them dry.
Use a ricer or potato masher to mash potatoes into tiny pieces.
In a large bowl, mix together the cream, butter, sugar and salt, then mix in potatoes. Beat with an electric mixer until fully blended.
Cover potato mixture loosely with parchment paper, and refrigerate overnight. This allows the potatoes to dry out slightly, which is desired.
Remove potatoes from refrigerator, and fold in flour until just incorporated.
Roll dough into golf ball-sized balls to make roughly 3 dozen lefse, or twice as large for 18 lefse. Keep balls of dough in refrigerator until ready to cook.
Heat a large cast iron skillet or griddle over medium-high heat.
Coat your work surface with flour. Roll a ball of dough in the flour, press the ball flat, then roll it as thin as possible with a rolling pin.
Use a large, thin spatula to transfer the flat lefse to the hot skillet. Cook for 1-2 minutes, or until small bubbles appear.
Flip the lefse, and cook another 45 seconds. Remove from skillet, then place on a clean dish towel or paper towel, covering with another towel to keep warm.
Cook the remaining balls of dough, placing each between the two towels after removing from the griddle.
Spread with butter and sugar if desired. Roll up before serving. Enjoy!