Carefully cook the potatoes in their skins until they are almost cooked (if you prick with a fork, you still have to feel resistance). Peel and cut into not too thin slices. Put plenty of vegetable oil and a little butter in a good pan. Fry the potatoes slowly until they are nice and brown and crispy (may take half an hour), remove them, possibly add a little more oil to the pan. Turn the diced onion in flour, shake off the flour, fry the diced onion in the very hot fat until golden brown.
Remove, drain the fat, put the potatoes and onions back into the pan, cut the black pudding and liver sausage into cubes and add to the fried potatoes, heat slowly in the pan.
It is very important that it is a bacon-free blood sausage, otherwise the dish will be too fatty.