Place cucumber slices and basil leaves in the cocktail shaker.
Use the muddler to press and twist the cucumber and basil gently until they release their oils and juice.
Add gin, lime juice, and simple syrup to the shaker.
Fill the shaker with ice and shake for 10-15 seconds until well chilled.
Double strain into an ice-filled glass to remove small herb pieces.
Top with a splash of club soda and stir once.
Garnish with a cucumber slice and basil leaf.
Notes
Store fresh basil wrapped in damp paper towels in the fridge for up to 5 days.Select firm, dark green cucumbers for the best flavor. English cucumbers work great for this recipe.Make simple syrup by combining equal parts sugar and hot water. Stir until dissolved and cool before using.The drink can be made without alcohol by replacing gin with cucumber-flavored sparkling water.