I'm sure everyone's seen this - that brownish stuff left behind when you grease an area of a baking dish that gets left exposed to the heat. Soap doesn't bother it too much, and it likes to gum up my scrubber. What's going on there, and are there any easy ways to get it off?
When oil gets overheated, it turns into a polymer that is insoluble in water, even with soap.
The best way to clean this up is with Barkeeper's Friend, Bon Ami, or a similar solvent (I think they're all alkaline-based solvents). It's non-abrasive, and safe to use on almost all cookware without leaving marks.
Edit: To help prevent this from happening in the future, use a paper towel to wipe off any excess baking spray on the edges of the baking dish that won't be covered by food.
I don't know of any method for the burnt-on oil in particular, but for difficult to clean pans in general, I usually resort to razor blades (not cartridge ones though). Something like a proper scraper tool would be even better.
Basically, something really sharp that can get underneath the substance, and then it can't help but come off.
Chemically, I'm assuming the stuff left on the pan after the cooking process wouldn't be the oil, since that comes off in soap. I suspect (guessing here) that it's the propellant from the can. Which isn't really that much of a pleasant thought.
Place your baking dish in a larger baking pan & squeeze soap dish over it plus a couple of handfuls of baking soda then add hot water to cover the dirty baking dish. Let it soak for an hour of so then just scrub with a brush & that's it!
You can buy a large box of baking soda at Smart & Final or Sam's Club or Costco. The baking soda will not scratch your baking dish.
Plain oil painter's turpentine does the trick. Thins the oil, dissolves residue...discard excess liquid oil, apply turps with an old bristle type paint brush. Thick caked-on gunk (like an abused deep fryer) may take a couple of applications or soaking but unlikely to have to wait "overnight". Turps isn't gritty and gets in the finest cracks to displace plasticized oils so fine polished finish on stainless steel isn't blemished with scratches from grit based cleaning products. Wipe with paper towel. Clean residual turps "smell" off appliance with any dishwashing detergent or methylated spirits for extra clean.