In a medium bowl, stir together flour and mashed potatoes until it looks as if they'll form a dough. Turn out onto a clean work surface, and, with the aid of a dough scraper, knead about 20 times so you have a smooth, but soft, dough.

Shape into a disc, wrap in plastic, and refrigerate at least 2 hours.

Heat a griddle, or heavy bottomed skillet, over medium heat.

Divide dough into 8 equal pieces and shape each into a disc.

Working with one disc at a time, on a heavily floured work surface, roll into an 8- to 9-inch circle. Place on griddle and cook until beginning to brown in spots, about 2 minutes. Flip and cook until the other side is browned in spots, another 2 minutes. Place on a plate while you continue making lefse.