Put 2 ozs. of butter and the beef marrow in a deep frying pan, and when hot add the chopped onion and cook till it begins to brown. Then add the rice, stir well, cook for 15 minutes, add the boiling stock, the white wine, a good pinch of saffron, salt and pepper, and mix all well. Simmer gently for 20 to 30 minutes, stirring occasionally, and just before serving sprinkle with the grated cheese and 2 ozs. of melted butter.