4 medium sweet potatoes (3 pounds), peeled and sliced 1 1/2 inch thick
1/2 teaspoon salt
3/4 teaspoon freshly ground pepper
3 tablespoons unsalted butter, cut into 1/2-inch pieces
1/3 cup pure maple syrup
1/3 cup water
Preheat the oven to 400°. In a large saucepan, cover the sweet potato slices with water and bring to a boil. Reduce the heat to moderate and cook until just tender, about 5 minutes. Drain well.
Arrange the sweet potatoes in a large gratin dish. Season with the salt and pepper, then dot with the butter pieces. Drizzle the maple syrup over the sweet potatoes, sprinkle with the water and bake for 15 minutes. Turn the sweet potatoes over and bake for about 25 minutes longer, until they're tender and lightly browned. If necessary, broil the sweet potatoes for a minute or two before serving.