Cut each ripe passion fruit in half and scoop out the pulp and seeds into a blender.
Add 2 cups of cold water and granulated sugar to the blender, blend on high for 30–60 seconds until pulp separates from seeds.
Place a fine-mesh sieve over a pitcher, pour the blended mixture through it, and press down on solids to extract the juice. Discard seeds and pulp.
Add the remaining 1 cup of cold water to the strained juice, stir, taste and adjust sweetness or dilution as desired.
Chill the juice in the refrigerator for at least 30 minutes or serve immediately over ice.
Garnish with fresh mint sprigs if desired and serve.