Most countries around the world have some kind of blood pudding. Within Spain, there are regional variations too, but the morcilla from Burgos in northern Spain is reckoned to be the best. Morcilla de Burgos is unusual in that it includes lots of onion and rice, and the fat is melted lard rather than the small dice of hard back fat. I've been to Burgos. I bought 1 kilo of artesanal morcilla. It really is the best.
A couple of metres of natural hog casing, 36-40mm diameter.