Method
Planking fish like this is particularly suited to a camp fire (i.e. an open fire on the ground) but it can be done on a conventional barbecue too. The fire needs to be hot embers and gently smoking wood; the odd flame is fine. Soak the plank in some fresh water for an hour or so; this will stop it catching in the heat of the fire. It’s good if it smoulders, but not if it erupts in flames.
Place the soaked plank on the ground and arrange the herbs and lemon slices down the centre. Lay the fish, skin side down, on top, rub it with olive oil or butter and season well with salt and pepper. Secure the fish in place with 4 or 5 steel nails.
You’re going to set the plank upright in the embers, so clear away the burning wood from a small semi-circular area, downwind of the hottest and flamiest part of the fire, so that any breeze will carry the heat and smoke towards the fish.
Using a log, carefully prop up the plank in the fire, in the cleared area. The fish should be on the upward-facing side of the plank, with the thickest part of the fillet nearest the ground. Leave it to cook gently for about 25–30 minutes. The base of the plank may start to smoulder; if it ignites, extinguish it with a splash of water.
When the fish is cooked, lift the plank out of the fire and set it directly on the table (you might want to douse the scorched base in water first). Let everyone dig in then and there. Good bread, lemon juice and mayonnaise are all you need alongside.