Peel and boil sweet potatoes until fork-tender, then drain well. Mash thoroughly or pass through a ricer to ensure no lumps remain.

In a large bowl, combine the hot mashed sweet potatoes with the melted unsalted butter, heavy cream, sugar, cardamom, and salt. Mix well.

Cover the mixture and refrigerate until completely cold (at least 2 hours or overnight); this is crucial for the dough texture.

Once chilled, stir in the flour gradually until a soft, workable dough forms. Do not overwork the dough or it will become tough.

Divide the dough into 16 walnut-sized balls. Dust a pastry board and rolling pin generously with flour.

Roll each ball out as thin as possible into a circle (approx. 6-8 inches), lifting and adding flour underneath frequently to prevent sticking.

Heat a dry non-stick skillet or griddle over medium-high heat. Cook each lefse for 1-2 minutes per side until speckled with brown spots.

Transfer cooked lefse to a clean towel and cover to keep them soft while you cook the rest.

In a small bowl, whip the softened salted butter with the maple syrup until fluffy.

Spread the maple butter onto warm lefse, roll them into cylinders, and serve immediately.