Saute onion in margarine. Blend in flour and seasonings. Gradually add milk; cool, stirring constantly until thickened. Add 1-1/2 cups cheese; stir until melted. Toss potatoes in cheese sauce. Pour into 2-quart casserole, reserving 1 cup potato slices. Arrange ham and remaining potato slices on top of casserole. Bake at 350 degrees for 30 minutes. Top with remaining cheese. From My Family's Favorites by Mary Beth Roe, QVC host. Formatted for MM by Pegg Seevers 6/8/96 -----