1 cup plus 2 tablespoons tonic water
1 envelope (1/4 ounce) unflavored powdered gelatin
2 tablespoons granulated sugar
3/4 cup gin
1 tablespoon fresh lime juice
1 tablespoon rosewater (optional)
Special equipment: UV black light
Bring the tonic water to a boil in a small saucepan. Place the gelatin and sugar in a medium heatproof bowl and add the hot tonic water. Continue stirring until dissolved completely, about two minutes. Let cool to room temperature.
Add the gin, lime juice, and rosewater if using. Divide mixture among shot glasses. Refrigerate until set. Turn on the black light when ready to serve and watch them glow.