A couple of times I've left things cooking a drop too long - and all the water evaporated and the food started to burn. Once it was potatoes; once apples. Both times I caught it pretty quickly and most of it came off, but now I'm left with slight scorch marks on the bottom and one of the sides of my pot - small burnt-looking black patches. Is there anything to do to get rid of them? (The pot is made of stainless steel.) I've tried cooking water and dishwashing soap in the pot, but it didn't really help. Any other ideas?