01 - Strain the fresh watermelon juice through a fine mesh sieve to remove all pulp and seeds, 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 strained watermelon juice into the saucepan while whisking continuously until the mixture is completely smooth and lump-free.
04 - Stir in the fresh lemon zest and vanilla extract, ensuring even distribution throughout the mixture.
05 - Place the saucepan over medium heat, stirring constantly to prevent scorching. Cook for 8-10 minutes until the mixture reaches a soft pudding consistency and thickens noticeably.
06 - Remove from heat immediately. If using, fold in the mini dark chocolate chips to create the traditional seed-like appearance throughout the pudding.
07 - Pour the warm pudding into individual serving glasses or molds. Allow to cool completely to room temperature, then refrigerate for at least 3 hours until fully set.
08 - Just before serving, sprinkle the surface generously with finely chopped pistachios. Add dried rose petals and extra chocolate chips as desired for presentation.