I made some pot roast in my Le Crueset caserole the other day -- brisket, red wine, tomato sauce, onion, carrot, and seasoning -- and burn the stuff at the bottom of the pot. Normally it cleans so easily, but now I have this charred black stuff at the bottom that isn't coming off. I soaked it overnight and put some elbow grease into sponging it, but to no avail. Does anyone have any tricks, tips, or suggestions? Should I (not) use a steal or copper wire pad? Any solvents?