Pre-heat oven to 210c (410f).
If your prawns are really large, you can snip the base near the tail and remove the vein along the back, leaving the rest of the shell intact.
Place in an oven proof baking dish and sprinkle with the butter cubes and pepper.
Place in the oven for approximately 3-4 minutes. Turn over and cook for another 3-4 minutes. Cooking time will depend on the size of your prawns, but they should be just starting to turn pink and curl up.
Add the lemon juice and place under a hot grill (broiler) to finish for a minute or so.
Serve with a sprinkle of sea salt flakes and coriander leaves, dipping the prawns into the lovely juice!