01 - Strain the fresh watermelon juice through a fine mesh sieve to remove all pulp and seed remnants, ensuring a smooth liquid base.
02 - In a medium saucepan, whisk together the granulated sugar and cornstarch until thoroughly blended and no lumps remain.
03 - Gradually pour the watermelon juice into the saucepan while whisking continuously, creating a smooth, lump-free mixture.
04 - Stir in the lemon zest and vanilla extract or vanilla powder, ensuring even distribution throughout the mixture.
05 - Place the saucepan over medium heat, stirring constantly to prevent scorching. Continue cooking for 8-10 minutes until the mixture achieves a soft, pudding-like consistency that coats the back of a spoon.
06 - Remove from heat source. If using, fold in the dark chocolate chips or chopped chocolate while the pudding is still warm, allowing them to create the traditional seeded appearance.
07 - Pour the warm pudding evenly into serving glasses or molds. Allow to cool completely at room temperature, then transfer to the refrigerator and chill for at least 3 hours until fully set and firm.
08 - Just before serving, sprinkle the tops generously with finely chopped pistachios. Optionally add dried rose petals and additional dark chocolate chips for visual appeal and extra texture.