First, add mint leaves and blackberries into a cocktail shaker, then muddle. 

Add the ice, sweetened lime juice, and brown sugar syrup. 

Secure the lid and shake vigorously for 30 seconds.

Fill a rocks glass with ice and add ginger beer 1/3 of the glass.

Pour the berry mixture into the glass.

Garnish with a fresh mint or basil sprig and a single fresh blackberry on a cocktail stick.

Serve.