Place gin, Violet liqueur, Cointreau, lemon juice and egg white in a cocktail shaker and dry shake (no ice) for 20 seconds.
Add ice and shake for 10 seconds.
Strain into a coupe or Nick and Nora glass.
Notes
Can’t find Empress 1908 Indigo Gin? You can use any gin (preferably a floral one) but you will not have quite the purple color. Note that the butterfly pea blossoms that color this gin don’t add any noticeable flavor.