In a 6 quart saucepan, melt 4 tablespoons butter with marrow and onion and cook over medium heat until onion is soft but not browned. Add all the rice and, stirring regularly, cook until opaque, about 2 to 3 minutes. Add a 6ounce ladle of hot stock, 1/2 cup red wine and saffron and bring to a boil. Stirring constantly, cook until stock level goes below level of rice. Add another 6ounce ladle and repeat the process for 16 minutes, until rice is "al dente", yet creamy and tender. Remove from heat and add cheese and remaining butter. Season to taste and serve immediately with stufato.