Add gin, lemon juice, raspberry syrup, simple syrup (if using), and egg white to a cocktail shaker.
Shake vigorously without ice (dry shake) for about 10 seconds to emulsify the egg white.
Add ice to the shaker and shake again until well chilled.
Strain into a chilled coupe or cocktail glass.
Garnish with fresh raspberries, if desired. Serve immediately.