How to butterfly prawns:
. Leaving the shell on, plunge the tip of a sharp knife through the the top, do the head first then the body, holding the prawn on either side to keep it stable.
. Open the prawn out flat. You'll see the intestinal tract running down the length of the prawn along the cut edge. Pull it out. It won't do you any harm to eat it if you leave it in. The 'goo' in the head area is fine - this is where the main flavour of the prawn is.
. Put the prawn shell side down onto a hot grill. Sprinkle with a little salt and pepper. They cook quickly - when the flesh turns white it's ready. If cooked flesh side down the prawn will become tough.
How to peel prawns:
. Twist the head off. Peel off the shell pulling it away from the belly. Leave the tail on for decoration if you like.
Larger prawns with thicker shells:
. Twist the head off. Pinch the prawn all the way along the body to loosen up the shell. Then carefully peel of the shell as above. After a certain point (about halfway along) the prawn should just slide out from the shell.
. Save the shells to make prawn soup. Put them in a bag and keep in the freezer.