Place the watermelon chunks into the blender and add fresh mint leaves if using.
4 cups watermelon chunks
Blend on high speed until the mixture is completely smooth and vibrant red, with no large chunks remaining. This should take about 30 seconds to 1 minute.
Pour the blended mixture evenly into the ice pop molds, leaving about 0.5 inch of space at the top to allow for expansion during freezing.
Insert the popsicle sticks into the molds, ensuring they are centered and straight. Place the molds on a flat surface in the freezer.
Freeze the popsicles for at least 4 hours, or until fully solid. The mixture should be firm and have a glossy appearance, with no visible liquid.
To serve, run warm water briefly over the outside of the molds to loosen the popsicles, then gently pull them out. Enjoy immediately for best texture.