Pressure cooker burnt

Hi there, I have a vintage hand me down made in France SEB pressure cooker I've been using for years. The other day I tried to steam some potatoes using a basket with water on the bottom. I left it too long and it totally burnt the bottom. I tried easy off - sprayed on and left a few days covered by mistake. Now it's a hardened crud that's even worse than the original burnt stuff. I've had good luck with easy off before, but I never tried it on this "family heirloom" and I don't know what to do to save it. Soaked for hours with dish liquid. Still got hard crud on there. I'm thinking of putting in the oven and turning on the cleaning cycle (my step mom's suggestion).