Arrange sweet potatoes in an even layer in a 9-by-13-inch glass baking dish. Combine maple syrup, butter, lemon juice, salt and pepper in a small bowl. Pour the mixture over the sweet potatoes; toss to coat.
Cover and bake the sweet potatoes for 15 minutes. Uncover, stir and cook, stirring every 15 minutes, until tender and starting to turn brown, 45 to 50 minutes more.