How to Make It
Process watermelon, in batches, in a blender or food processor until smooth.
Combine concentrate and 2 mint sprigs, and cook in a saucepan over medium-high heat 10 minutes. Stir together watermelon puree and lemonade mixture; cover and chill 8 hours. Remove and discard mint. Stir and serve over ice. Garnish, if desired.