Put soft but not melted sorbet into a blender. (My personal favorite is mango but passion fruit is also very good - and you should experiment to find your favorite flavors. I have never tried this with chocolate sorbet but there is no reason why that wouldn't work.)
Pour in some Prosecco.
Blend until just mixed through (2-3 seconds at most).
Pour, drink, enjoy.
Experiment with the ratios to make it exactly to your liking - it will change depending on the sweetness levels of the sorbet and the Prosecco you are using. Be careful not to over-blend. The bubbles can survive short blend cycles, and their light fizz is what makes this drink really work.