Preheat oven to 400°F. Combine maple syrup, butter, lemon juice, salt and pepper in small bowl. Arrange sweet potatoes in an even layer in a glass baking dish and 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 brown, checking fairly often, 40 to 45 minutes more. When you're done, you can cover and refrigerate for up to 1 day. To reheat: bake at 350°F until hot, about 10 minutes.