Combine pisco, lemon juice, lime juice, simple syrup and egg white in a cocktail shaker. Shake for 1 to 2 minutes until frothy.
Add ice cubes and shake for 30 to 60 seconds.
Strain into a martini or coupe glass.
Top Angostura bitters to taste.
Notes
SIMPLE SYRUP 1 cup (8 ounces) water 1 cup granulated sugar Bring the water to a simmer in a saucepan set over medium-high heat. Add the sugar and stir until it completely dissolves. Remove the pan from the heat. Set aside to cool to room temperature. Pour the syrup into a clean 1-pint bottle, cap it and refrigerate it until needed. Makes 1½ cups and keeps two months or longer in the refrigerator.