Our oven is like everyone else's - it heats unevenly. So we took the suggestion and stopped at a home improvement store and picked up a single 12"x12" ceramic tile (cost: $0.94) and clipped it to the oven shelf with binder clips.
Yup, it works! Look at that luscious corn bread I baked this morning! It came out just like it does in a household oven.
Go get yourself a tile.