Add blackberries and basil leaves to the cocktail shaker.
Muddle gently until the berries release their juice.
Pour in the rum, lime juice, and simple syrup. Then, fill the shaker with ice.
Shake for 10-15 seconds until well chilled.
Double strain into a Collins glass filled with fresh ice.
Top with club soda and stir gently with a bar spoon.
Finally, garnish with fresh blackberries and a basil leaf.
Notes
The drink can be made ahead without the club soda and stored in the fridge for up to 2 hours.Fresh blackberries work best, but frozen ones can work in a pinch. Just let them thaw first.Adjust the simple syrup amount based on the sweetness of your blackberries.Store any leftover simple syrup in an airtight container in the fridge for up to 2 weeks.