01 - Fill a cocktail shaker with ice.
02 - Add gin, elderflower liqueur if using, fresh lemon juice, lemon zest, and simple syrup to the shaker.
03 - Vigorously shake the mixture for approximately 15 seconds.
04 - Strain the cocktail into a chilled glass filled with fresh ice.
05 - Top with chilled soda water and stir gently to combine.
06 - Decorate with a lemon twist and a fresh mint sprig if desired.