Add the egg white, infused gin, lemon juice and simple syrup to a cocktail shaker and fit with lid. 2. Shake vigorously for 30 seconds. 3. Add 1/2 cup ice to the shaker, fit with lid and shake for 1 minute more. 4. Fill a cocktail glass with ice, and strain the cocktail into the glass. 5. Top with lemon seltzer and garnish with lemon slice and rosemary sprig. Makes 1.