Add 40 ml genever, 20 ml lemon juice and 20 ml simple syrup to a shaker.
Fill the shaker with ice and shake hard for 10-12 seconds, until well chilled.
Strain into an ice-filled highball glass.
Top with 50 ml soda water and stir once gently to combine.
Add a straw and garnish with a lemon wheel.
Genever's malt-wine base gives this Collins more body than a gin version — shake hard but briefly, so the soda still has room to lift the drink.
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