Tartiflette is a French dish from the region of Savoy, where it belongs to a family of rich, comforting dishes not for the faint of cheese. To make, arrange a layer of thinly sliced cooked potatoes on the bottom of your buttered baking dish. Add sauteed onions and cooked bacon lardons. Top with a layer of reblochon cheese, then two more layers of potatoes and cheese. Bake for 20 to 25 minutes at 375 °F.