This cocktail is a basic riff of the Vesper, replacing the vodka with cucumber vodka. Combined with Hendricks gin, Square One cucumber vodka is a great compliment with the Cocchi Americano providing a bit of body.
1.5 oz Hendricks Gin
0.5 oz Square One Cucumber vodka
0.25 oz Cocchi Americano
With so few ingredients, preparation technique seems to matter more.
Stir using a chilled glass and "refrozen ice" per Tristan Stephenson's The Curious Bartender book. Using a chilled stirring glass combined with very cold ice makes for a silkier drink. The lower temperature of the ice, rather than melting does more of the chilling work. But then it will take longer to get to the proper dilution, but well worth the extra effort.
Strain into a chilled cocktail glass
This drink doesn't require a garnish, but a cucumber wheel floated on the top can work.