Remove the leaves from the head of radicchio, wash in tepid water and drain well. Cut into strips.
In a large saucepan, over medium heat, saute the onion in the olive oil and half the butter until translucent, 3 to 4 minutes. Add radicchio and saute an additional 2 to 3 minutes. Add the rice and lightly toast, stirring, 1 to 2 minutes. Deglaze the pan with the wine, scraping up all the bits that have stuck to the bottom of the pot with your spoon. Add the cinnamon. Add a cup of the stock, stirring constantly until all of the liquid is fully absorbed. Continue, adding stock one cup at a time as necessary, until the rice is cooked al dente, about 20 minutes. Take off the heat, stir in the remaining butter and cheese and serve immediately. Serves 4.