Keep the broth at a slow, steady simmer near the risotto pot. If using saffron strands, dissolve them in 1 cup (240 ml) hot broth or water.
In a broad, sturdy pot over medium-high heat, cook the marrow/pancetta/prosciutto with the onion, oil, and 1 tbsp of butter until the onion is translucent. Add the rice and stir thoroughly to coat the grains.
Add 1/2 cup (120 ml) simmering broth and cook by constant stirring, following the same method used for the basic white risotto: stir until the liquid is gone, then add more and continue.
After the rice has cooked 15 minutes, add half the dissolved saffron. Keep stirring and, when the pot is dry again, add the remaining saffron.
Continue cooking, stirring, until the rice is tender but firm to the bite and there is no more liquid in the pot.
Off heat, add black pepper, the remaining butter, and all the Parmesan. Stir until the cheese melts and clings to the rice. Taste and correct salt if needed. Serve promptly with extra cheese at the table.
