Turn the oven to its grill setting.
Grate the lemon zest on the medium-fine holes. Wash the parsley leaves, drying them thoroughly. Chop by hand as finely as you can. In a food processor, break the stale bread into medium-fine crumbs, not dust. Add all the remaining stuffing ingredients, except for the parsley, to the breadcrumbs and blend until thoroughly combined. If it forms into a lump, remove the lid and break it up a little with a spoon. When all is blended well, add the parsley and blend once more. Donâ€™t try to chop the parsley in the processor, as it will take on a chlorophyll taste. Not nice! Once chopped with a knife, when put in the blender the blades will not be able to chop it further.
Take each crayfish, holding it behind the front claws, at the armpits so to speak. It cannot nip you when held in this way. Hold it down on the table and put the tip of a long, sharp knife into the centre of its head. Push = crunch = dead. This manoeuvre will kill the crayfish instantly. Pick it up, holding the tail end. In the centre of the actual tail, take the middle piece and gently twist it between your thumb and forefinger. Pull away as you twist and the signalâ€™s waste sac should come out attached to the tailpiece. If it does not go according to plan, donâ€™t worry, they can be picked out with the tip of a knife once the crayfish have been split in half. Cut all the crayfish lengthways from tip to tail using the point you made in the head to start. When this is done, remove any waste sacs you did not previously remove.
Take an oven tray, your stuffing and a knife, and set them down next to the crayfish. Pick up a generous amount of the stuffing and paste it on the flesh side of each half crayfish. You really want a good teaspoonâ€™s worth per half. Lay them, side by side, on the tray as you prepare them. When all are done, sprinkle them all over with salt and put the tray beneath the grill. They will want to cook relatively close to the actual grill for about 4 minutes. They do not take long. The shells will go totally red, and if there is any remaining signs of dark brown or blue colouring, they are not ready and require a couple of minutes more.
When done, transfer them to a plate, stacking them up in rows, and serve with little lemon wedges. I think the red shells oozing with green butter look great. I like to accompany this with a cold pastis with ice and water.
LEFTOVERS: This butter will freeze well and when needed is a fine application to a rack of lamb or grilled chicken.