Combine the dry ingredients (cornmeal, flour, baking powder, salt and sugar) in a bowl and stir to distribute the baking powder.
Stir the mayonnaise, eggs, and milk into the dry ingredients and mix.
Prepare the yellow cake mix into batter form (adding eggs and milk, etc according to the packages instructions). Add the yellow cake mix batter to the corn bread batter up to a 1:1 ratio (or you can use less cake batter).
Grease/butter a baking pan. Bake for about 30 minutes or so until done.