This saffron risotto is inspired by Pellegrino Artusi's (from his 1891 cookbook) second and third variations for this Italian classic. Its special components (other than the saffron) are bone marrow, white wine, and stock (you can use any—vegetable, chicken, or beef, though I prefer the first two). I like to use unsalted stock as you can control the degree of saltiness you prefer more easily, but if you want to use a stock that is salted, you may want to omit the pinch of salt with the onions in the beginning. If you don't have bone marrow or intend to keep this vegetarian then you can definitely leave out the bone marrow (which adds a richer flavor), it does not need to be substituted with anything. This is enough for 6 servings as a first course or side (for example, to go with osso buco, the classic pairing), or 4 as a main dish. —Emiko
Steep the saffron threads in an espresso cup of the hot stock or freshly boiled water. Depending on how long you let it steep, you will get more or less intense color and flavor. Ideally, before adding it to the risotto, let it steep at the very minimum 15 minutes, but closer to 30 minutes is best.
Over low heat, melt half the butter and the bone marrow (if using) in a wide skillet. Add the chopped onion with a pinch of salt and cook gently to sweat the onion, until it is soft and translucent but not browned, about 5-10 minutes.
Add the rice and toss through the butter, stirring occasionally, until the rice is glistening and translucent around the edges, about 2 minutes.
Pour over the wine and turn the heat up to medium and let cook, stirring occasionally, until the wine has almost evaporated entirely. Then begin adding the stock, about a cup at first, and stir occasionally, allowing the rice to absorb the liquid. With the second cup, add the saffron and its liquid, then continue cooking in this same way, allowing the rice to absorb mostly all the liquid before adding more stock, until the rice is creamy and al dente—it should take a total of about 17 minutes to cook to this point. NOTE: You may or may not need all of the stock—if you run out, simply use water to finish the cooking.
About 2 minutes before taking the risotto off the heat, add salt to taste (remember Parmesan will be added), top up with a little more stock so that it is "all'onda," like a "wave," (you want to be able to take the risotto off the heat while it is creamy and thick but still fairly soupy—it seizes up quite quickly by the time you serve it and it begins to cool), and add the rest of the butter along with the Parmesan cheese.
Serve immediately with some freshly ground black pepper. If being eaten alone, serve with some more Parmesan cheese, if desired.