Limoncello Gelee

Sprinkle gelatin over cold water in a small bowl. Let stand until softened, about 5 minutes.

Heat Prosecco, limoncello, sparkling water, and sugar in a medium saucepan over medium heat, whisking occasionally, until sugar dissolves. Add lemon juice and softened gelatin, and whisk until gelatin dissolves.

Pour mixture into an 8-inch square baking dish. Refrigerate until set, at least 45 minutes (or overnight). Cut into 4 portions, and garnish with lemon slices and mint.