Variations are aplenty with the Pisco Sour. Some (perhaps the Chileans?) claim the egg whites are unnecessary, most recipes say to use lemon... but then one notes that South American Limon is closer to a lime. Some use 2-1 rich syrup, some use 1-1 simple syrup.
And no matter the makeup... Anthony Bordain would rather have a beer.
In the end, I just went with what I know I like... less sweet and more alcohol. Thus, the recipe from imbibe magazine (with a quick nod to the limon/lemon/lime issue).
3 oz Pisco
1 oz lemon and lime juice mixture
3/4 oz simple (1:1 ratio of water and sugar) syrup
1/2 egg white
4 drops angostura bitters
In a cocktail shaker, mix together pisco, lemon and lime juice (I did about 50/50), simple syrup, and egg white. Cover and shake.
Uncover and add ice (bigger ice cubes are better). Recover and shake.
Strain into a cocktail glass.
Drop 4 or so drops of angostura bitters onto the egg white foam in different spots around the drink. Use a toothpick and swirl them around for the nicely finished look.