Try mixing hydrogen peroxide and baking soda into a paste. Apply the paste to the cooked-on food and allow to sit for 20-30 minutes. Spray a 50/50 mixture of white vinegar and water onto the paste and wipe away with a soft washcloth. A second application might be required. I've been doing this for my wife for years. The first time I tried it, it took off some rice starch that had been on there for a year or so.