Add gin, fresh lemon juice, and simple syrup to a cocktail shaker.
Fill the shaker with ice and shake vigorously for 10–12 seconds until well chilled.
Strain into a chilled highball glass over fresh ice.
Top with a splash of soda water and stir gently once to integrate.
Garnish with a lemon slice on the rim and express a lemon zest twist over the drink before placing it on top.
Dry shaking the ingredients without ice before the main shake will create a slightly silkier texture - a useful technique if you're making a Silver Fizz variant with egg white. For the standard Gin Fizz, shake hard and strain quickly to preserve maximum carbonation from the soda.
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