Prepare simple syrup by combining equal parts sugar and water in small pot and heating until the sugar is dissolved.  Let cool and set aside. 

Juice limes and lemons for enough juice to make as many cocktails as you're planning 

To make one pisco sour combine 3 oz pisco, 1 oz simple syrup, 1/2 oz lemon juice, 1/2 oz lime juice, and egg white in a cocktail shaker over ice

Shake vigorously for 30-45 seconds and pour into high ball classes.  Make sure you shake out all the foam that's left at the bottom of the shaker

Dot with angostura bitters and serve!