Melt 3 tablespoons of butter. Peel the potatoes and slice thin on a mandoline or with a food processor fitted with a 1-millimeter slicing blade. In a bowl, toss potato slices with the butter, salt and pepper.
On a parchment lined baking sheet, place 2 ring molds 3 inches wide and 2 inches deep. Layer the potato slices in the molds, overlapping the slices. Bake in a preheated 400 degree oven for about 40 minutes until the bottom layer of potatoes is golden and crisp and the potatoes are cooked through.