- In a blender, purée all of the ingredients until smooth. Strain through a fine sieve. Compost the pulp. Refrigerate for 2 hours.
- Pour the mixture into an ice cream maker. Churn for 30 minutes, or according to the manufacturer’s instructions, until it resembles the texture of granita.
- Serve in glasses with spoons (see note). The slushie mixture can be kept chilled in the ice cream maker for up to 1 hour.
You can choose to either peel the cucumber or not. The peel will lend a stronger green hue to the slushie but also a subtle bitterness.
Elderflower syrup can be found in the ready-to-drink aisle of the supermarket. You can also use cane syrup or simple syrup (a syrup made from equal parts water and sugar).
When ready to serve, you can add a shot of alcohol, such as St-Germain or white rum.