1. Cola syrup: Softly boil 1 part cola and 1 part sugar at medium to low heat. Let reduce for 10 minutes. Let the syrup cool before use.
2. Add 5 black berries, cola syrup and x - x dashes of angostura aromatic bitters to a low-ball glass.
3. Muddle the ingredients together.
4. Add the gin, lemon juice and ice to a shaker and shake vigorously.
5. Fill the lowball glass with ice and strain the gin mixture into the glass over a spoon to separate the layers.
6. Garnish with a blackberry.