To prepare the garnish, cut into thick spears about 1”/2.5cm taller than your glass. Use a peeler (or mandoline) to thinly slice the cucumber lengthwise.
Add ice cubes to a collins or large rocks glass. Add the cucumber garnish. If aiming for a swirl of cucumber against the side of the glass, place the cucumber in first – use a chop stick or bar spoon to help position it before adding the ice.
In a mixing glass, muddle the basil leaves with the simple syrup.
Add the lemon juice, lime juice, and gin.
Add ice and shake for 30 seconds.
Strain into the prepared glass.
Top with soda water and serve.
Notes
*Simple Syrup recipe:Combine 1 cup/200g granulated sugar with 1 cup/235ml hot water. Stir until sugar is dissolved. Can be stored in a sealed container in the fridge for up to 1 week.