To make the risotto, heat the butter in a wide 4-quart/4-l pot over medium-low heat. Add the onion and sauté until it is translucent, stirring frequently. Add the rice and continue stirring so that the rice toasts. It should become opalescent after a couple of minutes.
Stir in ½ cup/100 ml wine and cook, stirring, until the wine has evaporated. Stir in the remaining wine, ½ cup/100 ml a