Combine first eight ingredients in a large bowl; mix well. Set aside. Place half of the potatoes in the bottom of a greased 8-in. square baking dish. Spread meat mixture evenly over potatoes. Firmly pat the remaining potatoes on top. Bake, uncovered, at 400 ° for 30 minutes or until the meat is cooked and the potatoes are lightly browned. Cut into squares. Serve with ketchup if desired.