Sparkling Watermelon Lemonade

Makes 6 drinks

Ingredients
4 cups cubed fresh watermelon (seeds removed)
5 to 6 tablespoons superfine sugar or to taste
1/2 cup fresh lemon juice
seltzer, well chilled
Fresh mint sprigs for garnish

Directions
In a blender combine the watermelon, sugar and lemon juice. Puree until very smooth. Taste and add additional sugar if desired. Divide mixture into six tall glasses filled with ice, top with seltzer, stir well and garnish with mint.