1. Bring a large pot of water to a boil then add prawns and salt.
2. Lower heat and simmer for about 6 minutes or until the prawns are no longer translucent.
3. Remove from heat and, in a strainer, run cold water over them.
4. Set on a large dish and place in refrigerator to cool.
5. Serve cold, with mayonnaise or lemon wedges.