Melt 2 1/2 tablespoons butter in a pan over low heat, add finely chopped onion and chopped bone marrow. Cook slowly without browning. Add rice and toast for one minute or until translucent.
Pour in white wine and stir until absorbed. Cover rice with hot meat broth and cook, stirring every once in a while and adding broth as necessary when absorbed. After about 12 minutes, dissolve saffron powder in 1 tablespoon of broth and stir into the rice. Season with salt and pepper.
Cook rice "al dente", remove from the heat and combine with the remaining butter and Parmigiano Reggiano. Stir until creamy and serve immediately.
Its simplicity and fragrance, blended with its slight oiliness, succulence and the slight sweetness provided by the rice, are well-balanced. A dry ruby-red wine with a bouquet of fresh fruit and spices that is not too high in alcohol content and is fairly mellow, rather fresh and low in tannins is a perfect accompaniment. Curtefranca Rosso D.O.C
Instead of marrow, using an excellent meat broth is preferred.