Clean the potatoes and cut into thin slices with the vegetable slicer. Place roof tiles in a buttered, flat baking dish. Salt and pepper. Cook the flakes of butter on top and in a preheated oven at 225 ° C for about 50 minutes. This gratin is ideal with steaks and everything pan-fried. Where the potato slices are on top of each other, they are nice and soft and nice and crispy around the edges.