Slice coarsely the leek, except a 4 or 5 cm long part you should set aside for decoration. Cook the sliced leek in a frying pan over moderate heat with a little oil. If the leeks get too dry add some vegetable broth.
While the leeks are cooking chop hazelnuts and lightly toast them in a pan over high heat for or grill in the oven for 5 minutes.
When the leeks will be soft, remove them from heat and blend them to obtain a smooth cream. Season the leek cream with salt and pepper to taste.
Put a generous drizzle of olive oil in a pan and add some small sage leaves; put them on medium heat and, as soon as they turn crispy, remove them from the pan and put them on a piece of kitchen paper.
In the same pan where you fried the sage leaves put the black rice and toast it for a few minutes, stirring occasionally on medium heat.
As you smell a light aroma of toasted rice add a scoop of vegetable broth and let it simmer over low heat for about 25 minutes, adding a little more broth every time the rice gets dry.
Cut the piece of leek you have set aside and and cut it into 3-4 mm thick slices. Cook them in the same pan where you cooked leek before. Be careful not to turn them and add a little water (or broth, if you have some left) to prevent them from sticking. When the leek slices are softened remove them from heat.
After 25 minutes add the leek cream to the Venere rice, add a little broth if it has got too dry and simmer 5 minutes more.
Leave the rice from the stove, season with the nutritional yeast or grated pecorino cheese.
Serve the risotto decorated with the leek slices, crispy sage leaves and crunchy toasted hazelnuts.