Remove the head, the shell (keep the tail’s shell), and de-vein the prawns. Clean and pat dry. Split each prawn lengthwise into 1 big piece from back down (don’t cut all the way through). Then slice crosswise into two pieces (one piece will have a tail and the other will not). Place in a bowl. Mix with the egg white, salt, and cornstarch. Marinate for about half an hour.