Place the raspberry sorbet and vodka in the bowl of an electric mixer fitted with the whisk attachment. Whisk on low speed for 30 seconds, until the mixture is smooth and creamy.
Spoon the sorbet mixture into 3 low cocktail glasses and, while beating with a fork, add enough Prosecco to each glass so the sorbet is still creamy but not thick. Add one small scoop of ice cream to each glass and top with another splash of Prosecco. (The sgroppino should be the texture of a light slushy. The ice cream will melt into the raspberry slush.) Serve immediately with a small spoon.