Risotto al Radicchio

Name: Risotto al Radicchio
Ingredients: 1 small head (about 250 grams) radicchio; 1/2 red onion, finely chopped; 4 tablespoons (60 grams) cold butter, divided; 1 1/2 cups (320 grams) risotto rice (vialone nano, arborio, carnaroli); 1 1/4 cups (310 ml) red wine, warmed; 4 cups (1 liter) unsalted vegetable stock, warmed; 1/2 cup (50 grams) finely grated grana or Parmesan cheese; salt and pepper to taste