1. Juice the blackberries, reserving ½ cup of the juice and discarding the pulp. In a saucepan over medium heat, combine the demerara sugar and 1 cup of water and stir until dissolved. Let cool. Measure ½ cup of the syrup and place in a container. Reserve the remaining syrup for another use. Add the ½ cup of fresh blackberry juice to the container and stir to combine.

2. Fill an Old-Fashioned glass with crushed ice. In a cocktail shaker filled with ice, combine the Fernet, Averna, lime juice and ¾ ounce of the blackberry syrup. Shake well and strain into the ice-filled Old-Fashioned glass. Garnish with a blackberry and the sprig of mint, and serve.