A french classic, this wonderfully rich and crispy potatoes gratin recipe can made with duck fat or butter. Recipe adapted from The Art of Simple Food by Alice Waters.
Preheat oven to 350 degrees F. Generously butter a small 6 x 9 x 2-inch baking dish.
Using a mandoline, slice potatoes into paper-thin 1/16″ slices.
Layer slices, like shingles, along bottom of prepared baking dish. Sprinkle with 1/4 teaspoon sea salt and several twists fresh ground pepper. Sprinkle with 1/3 of the cheese.
Do the same for the second layer. For the third and final layer, arrange potato slices, carefully pour milk over mixture, scatter 3 tablespoons of duck fat or butter, and sprinkle with 1/4 teaspoon sea salt and fresh ground pepper.
Bake 45 minutes. Remove dish from oven and use a spatula to press potatoes down into the milk. Scatter remaining cheese over the top, and place back in oven. Bake 15 minutes more, or until the edges are golden brown and the filling is bubbling.
Cool 7 - 10 minutes, slice, and serve.