Their gills should be of a fine red, their eyes full, and the whole fish stiff and bright; if the gills are of a faint color, the fish limber and wrinkled, they are not fresh.
Cut off then-heads, open them, and take out the roes and clean them thoroughly; rub them on the inside with a little pepper and salt, put the roes in again, season them (with a mixture of powdered allspice, black pepper, and salt, well rubbed together), and lay them close in a baking-pan, cover them with equal quantities of cold vinegar and water, tie them down with strong white paper doubled, and bake them for an hour in a slow oven. They will keep for a fortnight.
This fish loses its life as soon as it leaves the sea, and the fresher it is the better. Wash and clean them thoroughly (the fishmongers seldom do this sufficiently), put them into cold water with a handful of salt in it; let them rather simmer than boil; a small mackerel will be done enough in about a quarter of an hour; when the eye starts and the tail splits, they are done; do not let them stand in the water a moment after; they are so delicate that the heat of the water will break them.
Clean a fine large mackerel, wipe it on a dry cloth, and cut a long slit down the back; lay it on a clean gridiron, over a very clear, slow fire; when it is done on one side, turn it; be careful that it does not burn; send it up with fennel sauce; mix well together a little finely minced fennel and parsley, seasoned with a little pepper and salt, a bit of fresh butter, and when the mackerel are ready for the table, put some of this into each fish.
Split them down the back, and season them with pepper and salt; broil them, and serve with the following sauce; pick and wash some fennel, parsley, mint, thyme, and green onions; but use only a small quantity of each. Boil them tender in a little veal stock; then chop them up, and add to them some fresh butter, the liquor they were boiled in, some grated nutmeg, the juice of half a lemon, a little cayenne pepper, and salt. Let it boil, thicken it with flour, and serve in a sauce boat.