This is a delicious recipe I made for a girl's day a few weeks ago. Taken from Barefoot Contessa
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Mash about 30 mint leaves with a mortar and pestle.
Juice the watermelon with a blender (then strain) or a juicer if you have one.
Put the mashed mint int a pitcher with 2c of the watermelon juice 12 oz light rum (I used Bacardi), 1/2 cup of simple syrup, and 6 tbl fresh lime juice and mix!
Pour over ice and garnish with mint sprigs!