I've been having the same troubles. I don't have a tub large enough to soak, but that has to be the easiest. Try some boiling hot water with some automatic dishwasher soap. Cover, let soak.
Scrape with scraper, soak some more . Use Easy off if you want, but it costs the most and doesn't always cut through the crud. Its like cement. Easy off is good for grease and light crud.
I heard that peroixde and hot water works to loosen it. I doubt vinegar and baking soda will do much. I also heard amonia works, but I tried that with no noticable improvement.
I have gotten most of the crud off and am about to break out the razor blade..