"This makes such a festive cocktail to kick off your Thanksgiving cocktail hour! This recipe is for one, but line up flutes for all your guests and it's easy to make as many as you need. Make the rosemary simple syrup up to a week in advance. The rest of the cocktail is together in minutes."
Combine water, sugar, and rosemary leaves in a small saucepan. Bring to a boil, stirring until sugar dissolves. Reduce heat to low; let simmer for 1 minute. Remove from heat and let syrup steep, about 30 minutes.
Strain syrup into a sterilized glass jar. Cover and refrigerate until completely chilled, at least 20 minutes.
Drop sorbet into the bottom of a champagne flute. Pour 1 fluid ounce rosemary syrup and gin on top. Pour in Prosecco very slowly so that it does not overflow. Garnish with 1 cranberry and sprig of rosemary.