In a medium mixing bowl, combine the first 6 ingredients. Blend thoroughly. In a skillet, brown beef and onion; drain. In a greased baking dish, spread 1/2 the cornbread mixture. Cover this with all of the meat mixture. Sprinkle meat with cheese. Top with remaining cornbread mixture. Bake at 375 degrees for about 45 minutes, or until done. If desired, spread butter or margarine on top.