Watermelon Twist

8 cups chopped seedless watermelon (about 6 pounds)
1/2 cup freshly squeezed lime juice (about 4 limes)
2 tablespoons sugar, plus 2 tablespoons more, if needed1/2 cup vodka, (optional)Mint leaves

1. Working in batches, puree in blender watermelon with lime juice and sugar until smooth. Add more sugar, if needed.
   
2. Transfer puree to a pitcher; add vodka, if desired. Cover; chill until ready to serve.
   
3. Stir; pour into tumblers, over ice. Garnish with mint.