Step 1Muddle the cucumber, chervil leaves and lime juice together in a mortar.
Step 2Pour the mixture into a glass measuring cup or small pitcher and add the gin and vermouth. Allow to infuse for 5 minutes.
Step 3Add the ice cubes and stir until the drink is chilled. Strain into a chilled cocktail glass, pressing to extract any juices.
Step 4Garnish with a sprig of chervil and a peeled cucumber strip on a bamboo skewer.