In a deep large heavy saucepan, cook sweet potatoes in water to cover over moderate to high heat just until fork tender, about 25 minutes. Do not overcook; sweet potatoes should not be soft and mushy. Cool sweet potatoes until easy to handle, then peel and cut horizontally into ¼ to ½-inch thick slices. Arrange sweet potatoes in a shallow 2-quart baking dish lightly coated with non-caloric vegetable cooking spray and set aside while preparing sauce/glaze. (Or, prepare sauce/glaze while cooking sweet potatoes.)
In a small heavy saucepan, combine maple syrup, butter, cinnamon and nutmeg, if desired, and salt; cook, stirring constantly, over moderate heat until butter is melted. Pour hot syrup mixture evenly over sweet potatoes.
Bake, uncovered, in a preheated moderate oven (375 degrees F.) for 20 to 25 minutes or until sauce is bubbly hot and sweet potatoes are heated through, basting occasionally with syrup mixture. May scatter pecan halves or coarsely chopped pecans as desired over glazed sweet potatoes during last 7 to 8 minutes of baking, if desired. Serve immediately.
Variation: Add 1 cup drained cubed peeled fresh or canned pineapple to sweet potatoes before adding maple syrup mixture.