Mix coffee with cola, pour into a flat metal mould and place in the freezer. Leave to freeze for at least 3 hours, stirring with a fork through the slowly freezing coffee-coke mixture about every 20 minutes. Place dessert glasses in a cool place.
Before serving, scratch the now crumbly frozen granite with a fork and pour into glasses. Drizzle 1 tablespoon of cherry syrup over each and garnish with a cocktail cherry.