Combine sugar with 100 ml (approximately 2/5 cup) of water in a saucepan and boil for 5 minutes. Remove from heat, add espresso and let stand for about 1 hour.
Pour part of coffee mixture into a shallow metal or plastic container and put in the freezer. Pour the other part into an ice cube tray, freeze as well.
Stir granita every 20 minutes to prevent ice crystals from forming. Freeze for 2 hours.
Combine with coffee ice cubes and puree in a blender.
Place granita into 4 chilled glasses and garnish with mint and coffee beans. Serve.