The modern version of the Pisco Sour wasn't born until late 1920s, when bartender Mario Bruige added Angostura bitters and egg white. However, the Pisco Sour can trace its origins much further back to the creation of its base: the strong, brandy-like liquor, Pisco.
In cocktail shaker filled with ice, combine egg white, Pisco, simple syrup, and lemon juice. Shake vigorously for 15 seconds, until the egg white breaks down, and strain into an up glass. Top with a few drops of bitters.