01 - Strain the fresh watermelon juice through a fine mesh sieve to remove all pulp and seeds, ensuring a smooth base for the pudding.
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 to prevent clumping and create a smooth mixture.
04 - Stir in the lemon zest and vanilla extract (or vanilla powder) until evenly distributed throughout the mixture.
05 - Place the saucepan over medium heat and stir constantly. Cook for 8-10 minutes until the mixture thickens to a soft pudding consistency that coats the back of a spoon.
06 - Remove from heat and fold in the mini dark chocolate chips if using, which will simulate the appearance of watermelon seeds.
07 - Pour the pudding into individual serving glasses or molds. Allow to cool to room temperature, then refrigerate for at least 3 hours until fully set and firm.
08 - Just before serving, sprinkle the top with finely chopped pistachios. Add dried rose petals and extra chocolate chips if desired for presentation.