Risotto alla Milanese Saffron Risotto

Name: Risotto alla Milanese (Saffron Risotto)
Ingredients: 1 pinch dried saffron threads; 8 cups (2 litres) warmed stock (unsalted vegetable, chicken or beef); 1/3 cup (80 grams) butter; 2 1/2 tablespoons bone marrow (optional); 1 yellow onion, finely chopped; 1 pound (450 grams) arborio rice (or carnaroli or vialone nano rice); 2/3 cup (150 ml) dry white wine; 1 handful (about 50 grams) freshly grated Parmesan cheese; salt and pepper to taste