Preparing them couldn’t be simpler. Preheat the oven to 400°F (200°C), wash and thoroughly dry the potatoes, then prick each one with a fork so steam can escape. Rub the skins lightly with oil or butter, season with salt, and place them on the oven rack or a baking sheet. Bake for 45 to 60 minutes, until a fork slides easily into the center and the skins feel firm and crisp.