6 large Granny Smith apples (3 pounds)peeled, halved, cored, and sliced
2 cups pure maple syrup
1 1/2 cups apple cider
1 stick (4 ounces) unsalted butter
1 teaspoon salt
Preheat the oven to 350°. Grease 2 very large, shallow baking dishes using 2 tablespoons of the butter. Alternating the sweet potato and apple slices, arrange the slices in the baking dishes in a single layer of concentric circles.
In a medium saucepan, combine the maple syrup, cider, butter, and salt. Simmer over moderate heat for 5 minutes. Pour half of the mixture over the slices in each of the baking dishes and cover the dishes securely with foil.
Bake in the center of the oven for 40 minutes, or until the apples release their liquid. Remove the dishes from the oven, uncover and baste the apples and sweet potatoes with the pan juices. Increase the oven temperature to 450° and place the dishes in the upper third of the oven. Continue baking for about 35 minutes longer, basting a few more times, until the sweet potatoes are tender and nicely glazed. Serve hot.
The recipe can be prepared up to 1 day in advance and refrigerated. Reheat, covered, in a 400° oven for 25 minutes.