Add sugar, 1 c water, and lemon zest to med saucepan over med heat, stir until sugar dissolves.

Stir in 1 1/2 cups cold water, lemon juice, and limoncello. Place in fridge until chilled, 2 hrs.

Add cold lemon mixture to ice cream maker until looks like soft serve. Remove to plastic lidded container and place in freezer until firm. 3 hrs.

Add a small scoop of sorbet to each champagne flute. Top with Prosecco and garnish with a sprig of mint.