Peel the potatoes; halve lengthwise. Arrange pieces in a 13x9x2-inch baking dish (3-quart rectangular).
In a medium saucepan, melt butter or margarine. Stir in brown sugar or granulated sugar, cornstarch, salt, and nutmeg, if you like. Stir in orange peel and juice. Cook and stir over medium heat until thickened and bubbly.
Pour sauce over the sweet potato pieces. Bake, covered, in a 400 degree F oven for 40 to 45 minutes or until potatoes are tender, spooning liquid over potatoes once. To serve, spoon sauce over potatoes. Makes 6 servings.