The basics are not hard. You take either apples or onions, cut them finely and cook them in lard. Then you drain them in put them in a bowl. Next you dice, or grind, a good bit of pork fat. If you dice it it will look better in the finished product. You add that to the bowl. Then you get to make your choices. In France, where I have done most of my blood sausage making, binders are generally not added, but in other cultures they are. You can choose various grains, rice, whatever, or none at all. You can also add some meat. Generally you want to use blood meat and very gelatinous cuts which you have already cooked to soften, but then these are the meats you would use for scrapple as well, and that is your local dish, so you may skip this part. I think it adds a lot. Then you season with spices, generally quatre epices, white pepper and some salt, again I learned in France, you puree the blood in a blender and strain it into the mixture. It is very liquid at this point. You then pass it all through a relative wide mouthed funnel into casings, you tie the casings off rather than twist, but leave a little flex in them, then you put directly in 80C water. If anything floats early, prick it. Cook until done through, then let cool at room temp, then in cold water. Then add ice. You want to do the cooling step by step because you end up with a more homogenous result that way.
Have fun.
Edit: You can also add some cream, but that would make you a northerner in France.