Use a sharp knife to cut the watermelon into 1-inch cubes, ensuring the flesh is free of seeds. Transfer the cubes into the blender jug.
4 cups watermelon flesh, cubed
Add the freshly squeezed lime juice and fresh mint leaves to the blender. Place the lid securely on the blender.
4 cups watermelon flesh, cubed
Pour in the ice cubes into the blender, ensuring the mixture will be chilled and slightly frosty.
4 cups watermelon flesh, cubed
Blend on high speed until the mixture is smooth, glossy, and thick, about 30-45 seconds. The color should be vibrant green-red and the texture uniformly creamy with no large ice chunks remaining.
Pour the smoothie into glasses, watching for a thick, glossy consistency with tiny ice crystals, and garnish with a mint sprig if desired.