In a medium saucepan bring the shrimp stock to a boil. Stir in the leeks until all are submerged and cook for 1 1/2 minutes until leeks are tender. Transfer to a blender and add the cubed butter. Blend until the butter is melted, then add the ice cubes with the blender still running. Blend until smooth. Pass through a chinois. Season with salt and pepper;
Peel and segment the oranges, making sure to remove the tough and bitter white skin. Reserve 48 segments in a small mixing bowl;
If using shrimp place toothpick lengthwise down shrimp, this will keep the shrimp straight. Heat the olive oil in 2 large saute pans until it just begins to smoke. Add the shrimp or the langoustines and brown well on one side. Flip to the other side and cook for 5 seconds. Transfer to medium mixing bowl.
Recipe Courtesy of David McInerney, Executive Chef, One if by Land, Two if by Sea