Muddle the fresh blackberries and basil in the bottom of a cocktail shaker until they’re crushed to a pulp.

Pour in 1 oz of lemon juice, 1 oz of simple syrup, 2 oz of gin or vodka, and fill the shaker with ice.

Shake until the cocktail is frosty and well mixed.

Strain the cocktail mixture into a highball glass filled with crushed ice.

Top up the glass with club soda, and garnish the drink with a fresh blackberry and basil leaves.