I got a bunch of small, "decorative" quinces from the community garden. It's from Chaenomeles Japonica, Japanese Quince tree. Or rather a bush. They smell really nice, but you can't eat them, they're super sour. Just awful. Perhaps this is why hardly anyone tried to cook them. Mistake! They're perfectly good when cooked.
For the actual recipe I'll point you to your search engine of choice, because a) I don't remember it exactly, and b) don't want you to blame me for it coming out bad :P
Note: this recipe is also called Membrillo and is apparently quite popular in Spain
The process was basically like this: I cut them in half, removed seeds and put them in the pressure cooker for about 10 minutes. That was perfectly enough. Then I used an immersion blender and mashed them into a smooth paste. you might peel them first, but I didn't and it didn't matter. The next steps are crucial to make the cheese or jelly gain the desired consistency. You keep it on the heat to bubble, add sugar (I think about 1:1 but I might be wrong) and stir it until the paste changes color to kind of red or dark orange. When you're satisfied with how dense it is, pour it on a tray and let it cool down. You can also put it in jars and use as jam. It lasts long and doesn't spoil easily.
I added some crushed walnuts to it, which proved a good idea. Pics:
What to say, it was very tasty and you should totally try it!