In a cocktail shaker, using a muddler, crush 6 blackberries to extract as much juice as possible. Add the ice cubes, non-alcoholic gin, orgeat syrup, lemon juice and bitters. Mix vigorously for 1 minute. Strain into a sieve placed over a lowball glass filled with the crushed ice. Decorate with the remaining blackberries threaded onto a cocktail skewer and the bunch of mint.
