Step 1.
- Muddle the blackberries in a cocktail shaker.
Step 2.
- Add gin, lemon juice, and simple syrup to the shaker with ice.
Step 3.
- Shake well until chilled.
Step 4.
- Strain into a highball glass filled with ice.
Step 5.
- Top with club soda and gently stir.
Step 6.
- Garnish with a fresh blackberry and a sprig of mint.