Sweat the chopped onion in the butter in a larger saucepan until translucent. Sprinkle in the rice, stir in and add the red wine. Let it boil down, only then gradually pour in the broth. Season and cook the rice al dente over medium heat, stirring constantly.
Take the pot off the hob. Add some parmesan to the rice and mix in the cleaned, washed and cut radicchio. Sprinkle with the rest of the cheese and serve immediately.