Sweet Potato Gratin with Pecans

Either type of sweet potato-the red-skinned, orange-fleshed variety or the tan-skinned, meaty yellow ones sometimes sold as yams-can be used to make this gratin. The latter will produce a thicker, denser dish than the former, which will be thinner and creamier. Serve as part of a breakfast buffet, alongside eggs and bacon, or as a side dish for roast turkey or pork.