How to Make It
In a large saucepan, cover the potatoes with water and bring to a boil. Add a generous pinch of salt and boil over moderately high heat until tender, about 15 minutes. Drain the potatoes in a colander, shaking off any excess water.
In the same saucepan, melt the butter in the cream over moderately low heat. Remove from the heat. Press the potatoes through a ricer or a sieve into the saucepan and mix well. Season with 2 teaspoons of salt and 1/4 teaspoon of pepper. Scrape the mashed potatoes into a large bowl and let cool slightly. (You will have about 5 cups of mashed potatoes.)
Add the flour to the bowl and, using a rubber spatula, stir until well combined. Scrape out the dough onto a lightly floured surface and knead a few times, until smooth.
Line a rimmed baking sheet with parchment paper and lightly dust with flour. Scoop 2-tablespoon balls of the dough and place on the prepared baking sheet. (You will have about 45 balls of lefse dough.) Cover with plastic wrap and refrigerate until the dough is just firm, about 20 minutes.
On a heavily floured work surface, using a lightly floured rolling pin, roll a ball of dough to a 6 to 7-inch round. (The dough will be paper-thin.) Carefully transfer the round to an 8-inch square of parchment. Top with a second square of parchment and repeat with the remaining dough.
Lightly brush a large cast iron skillet or griddle with vegetable oil. Add 2 or 3 dough rounds at a time and cook over high heat, turning once, until golden-brown spots appear on both sides, about 4 minutes total. Transfer the lefse to a wire rack and repeat with the remaining dough.
Serve the lefse warm, with cultured butter and lingonberry or cherry jam.