In a medium saucepan, bring the chicken stock to a simmer. Reduce the heat to low and keep warm.
Meanwhile, in a large, wide pot over medium-low heat, melt 3 tablespoons of the butter. Add the onion and saute until softened and translucent, about 8-10 minutes. Add the rice and stir well. Add the sparkling wine and allow it to simmer, while stirring, until it has been absorbed by the rice, and there is no liquid left in the pan. Add 1 – 2 ladles of the warm stock to the pan, and simmer, stirring frequently, until almost completely absorbed. Repeat this process, adding 1 – 2 ladles of stock at a time and stirring frequently, until the rice is cooked, making sure that you wait until the liquid is almost completely absorbed before adding more. Once you have used all of the stock, taste the rice to make sure it is cooked but still has a bite to it. If you find your rice to be underdone, you can add more stock, again 1 – 2 ladles at a time until it is cooked to your liking. From start to finish, the whole process should take you between 20-25 minutes.
To finish, stir in the Parmigiano and remaining 1 tablespoon of butter. If you find the risotto is not loose enough, add a few drops of stock. Taste the risotto and add any salt and/or pepper if you would like.
Ladle the finished risotto into serving dishes and top with black truffle shavings.