Place the butter in a large bowl and beat with an electric mixer until pale and fluffy. Add ¼ cup + 1 tbsp tonic water and 4 cups confectioner’s sugar and mix until combined. Add the remaining 2 cups confectioner’s sugar and beat well.

Place the buttercream in a piping bag fitted with a large, round tip.

Pipe a large swirl of buttercream onto each cupcake. Transfer the cupcakes to the fridge for at least an hour, until the buttercream is very stiff.

In the meantime, make the glaze. Combine the jello and boiling water and whisk until the jello has fully dissolved. Add 1 cup chilled tonic water and whisk. Allow the jello to cool to room temperature, but not so cool that it starts to set.

Dunk the cupcakes into the glaze so that only the buttercream is getting coated. Alternatively, you can brush the glaze onto the cupcakes with a pastry brush. Place the cupcakes in the freezer until the glaze has set, then repeat 5 more times for a total of 6 layers of glaze. 6 layers will make the cupcakes glow the brightest!

Serve the cupcakes under a blacklight and watch them glow!