1 round medium red or yellow watermelon, scooped out to the rind with minimal pink showing, flesh reserved (about 9 cups total)
1 1/2 cups sugar
1 1/2 cups water
1 bunch mint leaves, plus some for garnish
2 cups lime juice, from about 1 dozen limes
2 1/2 cups white rum
2 quarts watermelon juice (from reserved watermelon punch bowl), puréed and strained
Combine the sugar and water in a small saucepan. Bring to a boil and simmer until the sugar has completely dissolved. Remove from the heat and cool completely.
In a blender or food processor, puree all the watermelon flesh and pour it back into the watermelon punch bowl.
In a small mixing bowl, muddle the mint leaves, simple syrup, lime juice and rum. Pour into the punch bowl and stir to combine it with the watermelon puree. Serve over ice and garnish with mint.