You can substitute shrimp for the langoustine.
To make the boxes: I use a sharp knife to cut around the edges and create a box with handles. See my illustration above in the post. (It might help to do a test using a square piece of paper so you can begin to understand the folds.) Use a little egg white to attach the strips to the bottom. Score the inside edge of the box with a sharp knife. Brush bottom with egg white, being careful the egg white doesn’t touch the sides or they won’t puff.