For the Blunzengröstl with spring onion, boil or steam the potato until soft. Then let cool, peel and cut into bite-sized pieces. Roughly clean the spring onion, cut off the heads with the roots and cut 6 pcs. into not too thin rings.
Cut open the black pudding, peel it and cut it into coarse pieces. Heat the butter in a pan and fry the onion rings in it a little. Now add the potato pieces to the onion and add some olive oil. Season with salt and cumin, chop the remaining spring onion as well and sprinkle over the Blunzengröstl.