Fry the chopped onion in butter until translucent. Then add the risotto rice and fry for 2 minutes, stirring constantly. Then add the white wine and turn the temperature down to medium heat.
Add the stock to the rice in portions and simmer on low to medium heat until the rice is soft. This takes about 18 to 20 minutes. Stir again and again and when the broth has been absorbed, add a little more.
Hold the black pudding briefly under warm water, peel off the skin, cut the sausage into small pieces, add to the risotto and stir until the black pudding is distributed in the risotto. I like it when pieces of the black pudding are still recognizable, so don`t stir too hard.
If you like, you can stir in the parmesan. Season to taste with salt and pepper and serve.