I use Cascade. Just put hot water in the pan and dump in some Cascade and let it sit overnight and in the morning it'll swish right out. No nasty fumes either. It also works great for the iced tea jar that won't come clean anymore. Sparkling clean by morning.

I would try the oven cleaner, either the kind that works with heat, (you can warm the pressure cooker 1st) or use the kine that doesn't use heat to clean

Oven cleaner is meant to be used on porcelain covered steel not aluminum. I'd read the label really carefully before I used it on aluminum.

Thank you for the suggestions.

It is usable - but I think the bottom is a bit warped.