I have tried to make coffee jelly with agar, but that was disappointing. Even high-quality beans did not get me any good result, compared with gelatin-based recipes: The texture is different, but it is mainly the taste that disturbed me. I expect, perhaps, to have a neutral base for the jelly, so that the coffee flavour remains plain and strong. I also like the smoothness of gelatin compared with, say, agar.  Is there a good combination of beans and ingredients to make a vegetarian coffee jelly?  Som extra details:   Tried with agar only. Hot coffee added to the mix. Temperature-room cooling, then fridge cooling.  
It is hard to tell from the picture, but this doesn't look like burned off seasoning, it is more like a burned on residue. If that's the case, you can try cleaning it some way. The problem is that physical cleaning methods probably won't be sufficient, chemical cleaning with alkali will damage the seasoning and chemical cleaning with acid, if the seasoning is compromised, can rust the pan a bit. So there is a high chance you will end up reseasoning.   If this really looks and feels like a buildup and not like exposed oxidised metal, my preference would be to soak in warm, not hot, acid. Vinegar or a citric acid solution should work well. Afterwards, try to scrub off with a stiff plastic brush.   If it doesn't go away, or the seasoning goes away too, or if this was missing seasoning from the beginning, you have to strip and reseason. We have several questions on the topic, and the Internet is also full of suggestions. I personally prefer doing it with lye (best results, strips both old seasoning and rust), owners of self-cleaning ovens like incinerating it, and there are a list of other methods to work with.  