Peel, wash, and drain six medium-sized potatoes; cut them into as thin slices as possible; then wash them well again. Take a flat mold large enough to contain the potatoes, butter it well; put in a layer of potatoes, then a very light layer of grated cheese; season with a very little salt, and the same of pepper. Cover with another layer of potatoes, season again the same as before (the whole not to exceed half a pinch of each); then spread half an ounce of butter over them. Place the mold in the oven, and cook for thirty minutes; remove, turn it upside down on a hot dish, unmold, and serve.