After 30 years careful ownership of my favourite LC, I took my eye off the ball and burnt some braised red cabbage I was reheating. The accompanying photo shows it after a boil up, scrape, and 6 hour soak with undiluted white vinegar, which has had no effect whatsoever. I'll try the same with baking powder next and report back (next weekend, as I'm not at this house during the week).
I partially blame my new and useless glass cooktop.
All suggestions welcome.