Serve this salad warm out of the oven or at room temperature.
Preheat oven to 350°.
Combine potato and onion in a 13 x 9-inch baking dish. Combine sugar and next 5 ingredients (sugar through pepper) in a small bowl. Pour over potato mixture; toss well. Cover and bake at 350° for 30 minutes; stir occasionally. Stir in apple; bake 15 minutes or until apple is tender. Uncover and bake an additional 5 minutes.