In a small sauce pan, combine the water, sugar and mint leaves over medium-high heat. Stir until the sugar dissolves, turn the heat off and let the mixture sit for 20 minutes.
Combine the pureed strawberries, prosecco and simple syrup in a 9x12 glass baking dish. Stir together and place in freezer for 2-3 hours, scraping the mixture with a fork every hour or so to break it into pieces.
Serve with a sprig of mint