Peel potatoes and slice paper thin. Coat a shallow casserole, or gratin dish with clarified butter. (Be sure casserole will hold the potatoes.) Arrange potato-slices in overlapping fashion in layers. Sprinkle each layer with salt, pepper, and nutmeg. Repeat layers until all potatoes are used.
Mash a small clove of garlic in a salad bowl with the spoon. Discar