Prep your glass: Fill a rocks glass with ice to chill while you build the drink.
Muddle the berries: In a cocktail shaker, add the blackberries and simple syrup.
Gently muddle until the berries release their juice. Avoid over-muddling the seeds.
Add the base: Pour in the bourbon, fresh lemon juice, and bitters.
Shake it up: Add ice to the shaker and shake hard for about 10–12 seconds until well chilled.
Strain: Dump the ice from your glass. Strain the cocktail over fresh ice.
For a smoother sip, use a fine strainer to catch seeds and pulp.
Top with fizz: Add a small splash of club soda to lift the flavors and give a gentle sparkle.
Garnish and serve: Add a lemon wheel or twist, a fresh blackberry, and a mint sprig if you like. Serve immediately.