Hack off the top of the shell with scissors or a small, sharp knife to about halfway down the back, removing the digestive tract that runs along the length of the langoustine.
Mix the butter, lemon juice and garlic in a bowl, then brush each langoustine with this mixture.
Place langoustines under a hot grill for 4-5 minutes or until they are done.
When cooked, remove from the grill, lift out the langoustines and put on a large plate. Pour over the rest of the butter mixture.
Serving Suggestions: Serve with lemon and chopped parsley.