Watermelon Basil Margaritas

7 1/2 pounds seedless watermelon, rind removed, fruit cut into 1-inch cubes
4 teaspoons superfine sugar
6 ounces (3/4 cup) silver tequila
24 basil leaves, plus sprigs for garnish
3 ounces (1/4 cup plus 2 tablespoons) triple sec
6 cups small ice cubes

Place 24 watermelon cubes on a baking sheet lined with parchment. Cover, and freeze at least 1 hour (up to 2 days).
Puree remaining watermelon and the sugar in a blender until smooth. Pass through a sieve lined with cheesecloth into a bowl. (You should have 3 cups.)
Place tequila and basil in a glass pitcher, and crush with a wooden spoon. Stir in watermelon juice and triple sec.

photo and recipe from Martha Stewart