Mix together the sugar and the water until it dissolves. bring to a boil.
Pour the simple syrup into a bowl and refrigerate until cold.
Meanwhile puree and strain the raspberries.
Add the lemon zest to the raspberries.
Pour up to 3/4 cup of the cooled simple syrup into the raspberry mixture and add the prosecco. (The amount of simple syrup will depend on how tart your raspberries are and how sweet you'd like the sorbet).
Mix in your ice cream maker according to the manufacturer's instructions.