1/2 cup fresh pink grapefruit juice (from 1 small grapefruit), plus 1 wedge for garnish
1/4 cup passion fruit puree, such as Goya
4 tablespoons dark rum
1 tablespoon superfine sugar
Place the ice cubes, grapefruit juice, passion fruit puree, dark rum, superfine sugar and seltzer in the pitcher of a blender and blend on high until smooth and slushy. Pour into a double old-fashioned glass and garnish with a wedge of fresh pink grapefruit.