Bring broth to simmer in a saucepan. Meanwhile, heat the butter and oil in a 4-quart casserole and sauté the onion for 1-2 minutes, until softened. Add the rice and stir for 1 minute. Add the wine and cook until it is all absorbed. Add the radicchio, and then start to add the simmering broth 1/2 cup at a time, letting each addition be completely absorbed before adding another 1/2 cup. Reserve 1/4 cup broth to be added at the end. This takes approximately 18 minutes to reach al dente stage. Then add the last 1/4 cup of broth and the Parmesan. Combine well and serve immediately.