Pierce potatoes with fork. Microwave on high for 14 to 16 minutes or until soft; cool slightly. Slice into 1/4-inch thick slices. Layer half the potatoes, onion, and cheese in 9-inch square baking dish. Repeat layers. In medium bowl, whisk together soup, milk, and pepper. Pour over potatoes. Bake uncovered in 350 degree oven for 40 to 45 minutes or until heated through and cheese is melted.
