Add the egg white or aquafaba to a dry cocktail shaker. Cover and shake vigorously for 30-40 seconds, until the egg white is foamy.
Pour in the gin, lemon juice, and simple syrup. Fill the cocktail shaker 3/4 of the way with ice. Cover and shake for another 30-40 seconds, until thoroughly chilled.
Strain your beverage into two cocktail glasses and enjoy responsibly.