A driftwood fire on a beach in the Hebrides, mackerel caught that day, filleted (put knife in behind the gills, turn towards its tail, then, following the backbone, pull the knife down towards the tail; flip over and repeat on the other side). When the embers are just so, place the mackerel, skin-side down, on the griddle. By the time the skin is happy and crispy, the fillets should be cooked.