Add pisco, lime juice, simple syrup (I add these first with ice and stir until chilled then remove ice) and egg white into a shaker and dry-shake (without ice) vigorously (blender works well pulsed).
Add ice and shake again until well-chilled (skip this step if you did ice first)
Strain into chilled glasses. Garnish with 3 to 5 drops of Angostura bitters. Using a straw, toothpick or similar implement, swirl the bitters into a simple design, if desired. Serve immediately.
