In a 12 to 14-inch skillet, heat the olive oil over medium heat. Add the onion and cook until softened and translucent but not browned, 8 to 10 minutes. Once the onions are translucent add the rice and stir with a wooden spoon until toasted and opaque, 3 to 4 minutes. Add the dried porcini.
Add the wine to the toasting rice, and then add a 4 to 6-ounce ladle of stock and cook, stirring, until it is absorbed. Continue adding the stock a ladle at a time, waiting until the liquid is absorbed before adding more. Just before adding the last 4 to 6-ounces of stock add the freshly sliced porcini. Cook until the rice is tender and creamy and yet still a little al dente, about 15 minutes. Stir in the butter and cheese until well mixed. Portion risotto into 4 warmed serving plates, serving with extra cheese.
Recipe copyright 2001, Mario Batali. All Rights Reserved.