1. Pour 500ml of milk, the pomegranate juice, and the molasses in a medium pot over low heat.
2. Remove from the heat and set aside for 20 minutes to infuse the milk with the pomegranate flavor.
3. Mix the remaining milk and the corn our in a small bowl.
4. Strain all the milk into a medium saucepan over medium heat. Add the sugar. Stir constantly until the milk starts to thicken, about 20 to 30 minutes.
5. Add the mastic and the rosewater, and stir continuously until the mixture becomes a thick custard, about 30 to 40 minutes.
6. Ladle the custard into bowls.
7. Set aside to cool at room temperature for 1 hour, then refrigerate for at least 2 hours before serving.
8. To garnish, top with pomegranate seeds and dried rose petals.