Combine all ingredients in a medium saucepan over medium high heat. Stir until the sugar is dissolved. Bring to a boil, then remove from heat, cover, and let sit for 15 minutes. Remove the mint sprigs. Pour the mixture into a blender and puree until smooth. Pour through a strainer into a medium bowl. Chill completely.

Freeze in an ice cream machine according to manufacturer's instruction. Sorbet will be very soft. Spoon into a medium bowl and let firm up in the freezer for at least 2 hours before serving.