In a small pot, bring the stock to a light simmer.
In the meantime, clean and prepare the radicchio. Slice the leaves into thin strips, dice the white part and discard the root.
Add extra virgin olive oil and onions to a large skillet. Sauté for a few minutes on medium-low heat.
Add the rice and stir for 30 seconds to toast the grains and coat them with oil. Then, deglaze with white wine.
When the wine is completely absorbed, start adding the stock one ladleful at a time. Stir frequently and wait for the rice to absorb the liquid before adding some more.
After around 10 minutes, add the radicchio to the rice. Keep just a little aside for garnishing; it gives the dish a nice crunch.
Continue cooking and adding the stock for another 10 minutes.
When the rice has a soft bite, turn off the heat. Add Gorgonzola, Parmesan cheese and salt and pepper to taste.
Stir vigorously to melt the cheese with the residual heat and create a creamy consistency.
Serve immediately, adding a few strips of fresh radicchio on top of each dish.