Add all ingredients to a crushed ice-filled shaker and shake for 30 seconds. Pour, unstrained, into a tall glass. Garnish with a spent lime half and a sprig of mint.
To make the syrup bring a cup each of water and demerara sugar to the boil and add 3 sticks of cinnamon and 10 allspice berries. Stir until dissolved then remove from heat and cover for 2 hours before straining.
I originally used a rum distilled in Key West with very limited availability (16 bottles total). I created this drink for the 2016 Hemmingway Look Alike Society winner Dave Hemmingway (no relation but the only winner with the same last name).