Add blackberries and mint leaves to the cocktail shaker.
Muddle gently to release the berry juice and mint oils.
Pour in vodka, simple syrup, and lemon juice.
Fill the shaker with ice and shake for 10-15 seconds.
Strain into a rocks glass filled with fresh ice.
Top with a splash of club soda.
Garnish with fresh blackberries and a mint sprig.
Notes
Fresh blackberries work best, but frozen can be used in a pinch. Just thaw them first.The drink can be made sweeter by adding more simple syrup.For a stronger mint flavor, add extra leaves during muddling.Store leftover simple syrup in the fridge for up to 2 weeks.Avoid over-muddling the mint leaves, which can make them bitter.