For the baked on stuff, I pour Simple Green (automotive version, but that really doesn't matter) right on the top in the wells, filling it up as much as possible, and let it sit. Mine is white, and my hubby used a Scotch brite pad on it once and scratched it up! So we don't scrub it anymore.

Simple Green is what I used to clean the popcorn kettle at the ballpark of a few seasons of scorched popcorn oil. I let it sit in there until the SG evaporated until it was more like a gel, and the gunk peeled right off.

Karen