In a cocktail shaker, muddle a few fresh blackberries.
Add the gin, blackberry puree, lemon juice, simple syrup, crème de mure, and egg white.
Dry shake (without ice) for about 15 seconds to emulsify the egg white.
Add ice to the shaker and shake again vigorously until well-chilled.
Double strain into a chilled coupe glass to ensure a smooth texture.
Allow the foam to settle for a minute.
Garnish with a skewered blackberry and a fresh mint leaf on top.