• Grind the saffron threads in a mortar and pestle, then add warm water or broth. Let infuse for at least 15 minutes, better if longer. (See Notes) If using saffron powder, smply dissolve it in warm water or broth.

Prepare the soffritto

• Sauté the onion or shallots and chopped bone marrow very gently in the butter until the marrow has melted and the onion has softened and turned traslucent.

Toast the rice

• Raise the heat to medium and add the rice. Let it sauté in the soffritto until it turns a chalky white. Take care that neither the onion or the rice browns.
• Add a splash of white wine and let it evaporate.

Simmer the rice in broth

• Proceed with the risotto in the usual way, adding a ladleful of broth to the rice and simmering until it evaporates. Then add another ladle at a time, repeating the process until your rice is al dente.
• About halfway through the cooking process, or if you prefer a more assertive flavor, about 5 minutes before the rice is done, add the saffron and its broth. Continue to cook as usual.

The final mantecatura (butter and cheese enrichment)

• While the rice is stlll fairly brothy, turn off the heat and add the grated parmigiano-reggiano and a knob of butter.
• Stir the rice around vigorously for a minute or two, until the butter and cheese have completely melted into the rice and you've developed a creamy texture.
• Pour on to a serving dish and serve right away.