Peel and finely chop the onion. Melt the fat in a pot. Sauté onion and rice in it. Deglaze with half of the stock and wine. Bring everything to the boil and simmer at low heat for about 20 minutes.
Add the remaining stock while stirring. Clean and wash the radicchio, cut into slices and fold into the risotto with 50 g parmesan. Season to taste with salt and pepper. Arrange the risotto on plates and serve garnished with remaining Parmesan and basil.