Arrange sweet potatoes in an even layer in a 9-by-13-inch glass baking dish. Combine Kahlua, butter, lemon juice, salt and pepper in small bowl. Pour the mixture over the sweet potatoes; toss to coat.
Cover dish with foil, and bake in preheated oven for 15 minutes. Uncover; stir potatoes and continue to bake. Stir every 15 minutes until potatoes are tender and starting to brown, 45 to 50 minutes more.