Preheat the oven to 400 degrees F (200 degrees C). Line an oven-safe skillet or baking pan with aluminum foil.

Poke the potato skin all over with a knife and place on the prepared pan.

Roast in the preheated oven until very tender and easily pierced with a knife, about 1 hour. Let sit until cool enough to handle but still very warm.

Scoop potato flesh out into a bowl. Mash smooth with the back of a spatula until there are no lumps left. You can also use a potato ricer. Add the butter and mix until it disappears. Add the salt, sugar, and cream; mix until smooth. Cover and refrigerate until chilled, about 2 hours.

Mix in flour in several additions until the dough is able to be kneaded by hand. Add enough flour to form a soft, but not too sticky, dough. You need to be able to roll it out fairly thin without it falling apart.

Wrap dough with plastic and refrigerate until chilled, about 1 hour.

Divide dough into 8 portions. Dust each with flour and roll out onto a well-floured kitchen towel to 1/8-inch thick, or thinner.

Heat a very lightly buttered nonstick pan over medium-high heat. Cook the lefse in the hot pan, poking the surface lightly with a fork, until golden brown blisters form, 2 to 3 minutes per side. Stack on a plate as they're cooked and keep covered with a towel. Serve warm.