Boiled Mackerel

Prepare and clean some mackerel, put them in salted water, and boil until they
are done. When they are cooked, drain the mackerel and put them on a hot dish.
Blanch some fennel in salted water, and when it is soft drain and chop it finely ; put
one tablespoonful in half a pint of butter sauce, and serve in a sauceboat with the fish.