Use a vegetable peeler to create one long cucumber ribbon for garnish. Set aside.
Place cucumber slices in a cocktail shaker and muddle gently to release the juice.
Add gin, elderflower liqueur, lime juice, and simple syrup to the shaker.
Fill shaker with ice and shake for 10-15 seconds until well chilled.
Strain mixture into an ice-filled highball glass using a fine mesh strainer.
Top with club soda and stir gently.
Garnish with the cucumber ribbon and mint sprig.
Notes
The drink can be made non-alcoholic by replacing gin with cucumber-infused water and elderflower liqueur with elderflower syrup.Fresh ingredients make a big difference - use newly cut cucumber slices for the best flavor.Store any leftover simple syrup in an airtight container in the refrigerator for up to 2 weeks.Pre-chill the highball