So into the pan went hot water and perhaps 1/4 cup of white vinegar along with a drop of dish washing liquid. This I put on to boil (didn't forget about it either) for about 20 minutes.
It worked like a charm. The stain practically melted off with a little help. So here is yet another use for vinegar.
The other stain remover is for cups that have caffeine stains. We drink tea and it does discolor our cups. The best thing I've found that is non-toxic is homemade soft scrub (basic recipe is baking soda mixed with good laundry detergent). You can find the recipe for my soft scrub here.