Step 1In a large bowl, stir together the Prosecco and sugar until the sugar is dissolved.
Step 2Into a medium bowl, push the raspberries through a strainer to remove any seeds. You should have a scant one-fourth cup puree.
Step 3Whisk the raspberry puree in with the Prosecco, then whisk in the rose water. Strain the mixture again to remove any raspberry solids to form the granita base. This makes about 5 cups.
Step 4Place the base in a large baking dish. Freeze, stirring every half-hour or so until the granita is frozen. To serve, shave the granita, raking the tines of a fork across the surface to break up the crystals. Serve immediately.