Open the fish sufficiently to admit of the insides being perfectly cleansed, but not more than is necessary for this purpose; empty them with care, lay the roes apart, and wash both them and the mackerel delicately clean. It is customary now to lay these, and the greater number of other fish as well, into cold water when they are to be boiled; formerly all were plunged at once into fast-boiling water. For such as are small and delicate, it should be hot; they should be brought gently to boil, and simmered until they are done; the scum should be cleared off as it rises, and the usual proportion of salt stirred into the water before the mackerel are put in. The roes are commonly replaced in the fish; but as they sometimes require more boiling than the mackerel themselves, it is better, when they are very large, to lay them upon the fish-plate by their sides. From fifteen to twenty minutes will generally be sufficient to boil a full-sized mackerel some will be done in less time; but they must be watched and lifted out as soon as the tails split, and the eyes are starting.
Dish them on a napkin, and send fennel or gooseberry sauce to table with them, and plain melted butter also.
Small mackerel, 10 to 15 minutes; large, 15 to 20 minutes.