In a cocktail shaker, combine the Pisco, lime juice, simple syrup, and egg white.
Shake all the ingredients vigorously without ice to help emulsify the egg white and create a frothy texture.
Add a few cubes of ice to the shaker and shake vigorously once more to chill the drink.
Strain the mixture into a chilled glass and garnish with a few dashes of Angostura bitters.