The pisco sour cocktail, invented in Peru around 1900, uses a pisco (Peruvian grape brandy) that has a bit of bite to it--that is, nothing too smooth--to create the balance in this creamy, frothy, limey drink.
A pisco sour is made in a cocktail shaker with simple syrup (not sugar, which will not dissolved properly). These measures are also a bit off, and you should use half a fresh egg whites to every serving pisco sour (i.e. 1 fresh egg white for every 2 pisco sours). You should also add the aromatic bitters to the ingredients list (can use Angostura bitters or Chilean amargos, which are slightly different but very similar).
Excellent recipe, just tried it and it was quite tasty!