Watermelon Agua Fresca

1 very ripe, red seedless watermelon,
about 12 lb.
Juice of 4 limes
3/4 cup sugar
1 cup crushed fresh mint leaves, plus
sprigs for garnish
4 cups sparkling water
3 limes, thinly sliced
2 quarts ice cubes

Cut the watermelon in half and, using a metal spoon, scoop out the flesh into a large bowl. Working in batches, puree the watermelon in a blender or food processor. As each batch is ready, transfer it to another large bowl. Add the lime juice, sugar and mint leaves to the puree, and stir to dissolve the sugar and combine the ingredients. Cover and let stand at room temperature for at least 1 hour or up to 3 hours to allow the flavors to develop. Pour the watermelon mixture through a medium-mesh sieve into a large, clear glass jar. Add the sparkling water, lime slices and ice. Ladle or pour into glasses and garnish each glass with a mint sprig.

by williams sonoma