In a frying pan, melt the butter (1). Sauté the onions in it until translucent. Pour in the long-grain rice and sauté, stirring, until the rice grains begin to crackle. Extinguish with Prosecco (1) and cook it completely while stirring.
Add the soup little by little and take up the long-grain rice while stirring frequently. The long-grain rice should be soft at the end, but still al dente at the core and the consistency of the risotto should be soupy. If necessary, add a little more liquid.
To finish, fold butter (2), lemon zest and Parmesan into the finished risotto and season with salt and pepper to taste. Immediately before serving, season the risotto with the Prosecco (2).