Heat the olive oil in a large heavy pot over medium heat. Add the onions and cook, stirring occasionally, until soft, 10 minutes.
In the meantime over low heat, in a saucepan on the back burner of the stove, bring the chicken stock and 1 1/2 cups water to just below a simmer. In another saucepan, warm the red wine just below a simmer.
Increase the heat to medium, add the rice to the onions and stir until the rice is very hot, just begins to stick to the bottom of the pan, and the rice is completely coated with oil, 2 to 3 minutes. Add two ladlefuls of hot red wine and stir constantly until the wine is almost absorbed. Add a ladleful of chicken stock and stir steadily to keep the rice from sticking. Continue to add the chicken stock a little at a time, stirring until the chicken stock is gone. Then continue with the hot red wine. Continue to add the red wine until the rice is at the chalky stage, 18 to 22 minutes. Continue to add wine and stir for an additional 2 minutes, until it is just beyond the chalky stage. If you run out of red wine, use hot water.
Remove the pan from the heat, add another ladleful of red wine, butter, nutmeg to taste, half of the Parmigiano Reggiano, radicchio and salt and pepper. Stir quickly, cover and let sit covered off the heat for 5 minutes.
After 5 minutes, stir the risotto. Season to taste with salt and pepper and serve immediately with more Parmigiano.