Wash and cut the radicchio into thin stripes and chop the onion. Heat a knob of butter in a pan and glaze first the onion and as soon as it gets soft, add the radicchio. when the radicchio changes its colour and is soft, add the rice and roast it for a few minutes on a high flame. Deglaze with the glass of white wine. Gradually add the vegetable broth, always letting it absorb before you add more.
Cut the Fontina into small cubes and melt it over a water bath and a low flame, gradually adding milk to the cheese. shortly before the cooking is terminated, add the fondue to the risotto, mixing everything well. turn off the flame and add the rest of the butter and the Parmigiano cheese. Serve with some of the chopped herbs sprinkled over the plate.