This is not the cloying, candylike sweet potato side dish that is so often topped with marshmallows. Here, the vegetable's distinctive, mellow sweetness (as well as that of the acorn squash) is augmented by hints of brown sugar and nutmeg, so that the ingredients speak for themselves. Slicing the vegetables rather than puréeing them also imparts a lovely presence—the squash looks like happy smiles, the sweet potatoes like shining coins.
Cooks' note:
Vegetables can be baked 1 day ahead and chilled. Reheat in a baking dish, covered, in oven.
