This feather-light chiffon pie has the subtle but distinct flavor of watermelon; as well it should, since there are nearly three cups of watermelon juice in the filling. That juice is thickened with gelatin, and then blended with whipped cream and beaten egg whites to give the filling that airy chiffon texture we all love. The pie makes a luscious summer dessert for any gathering of friends or family. It looks cool garnished with watermelon balls, but don’t garnish until the last moment to prevent juice buildup on the plates. This recipe is best made at the height of watermelon season. Cooking time is fridge time.