Heat the olive oil with the butter until hot over medium heat, and then cook the onions with some salt and pepper, stirring, until soft.
Stir in the rice; it will mix and get coated with the oil and become toasted and translucent.
Start adding your vegetable broth, 1 ladle at a time, stirring so the rice doesn't stick. When that's absorbed, keeping adding more until you are finished with the broth. Stir in the radicchio and cook 1 minute, and then begin ladling in the wine a little at a time until completely absorbed. The risotto will take about 16 to 18 minutes to cook. Remove from the heat, add your Parmigiano and mix well.