The CWI Cookbook

 Haddock, cleaned
Egg sauce (optional)
Pudding for stuffing (optional)

Wash it well, and put it on to boil, as directed for Boiled Cod. A haddock of three pounds will take about ten minutes after the kettle boils.
Haddocks, salted a day or two, are eaten with egg sauce. Or, if small, very well broiled, or baked, with a pudding in their belly, and some good gravy.
Obs.–A piscivorous epicure protests that “Haddock is the poorest fish that swims, and has neither the delicacy of the whiting, nor the juiciness of the cod.” Our experience goes to substantiate the same point.

The Cook’s Oracle by William Kitchiner, MD, New York, 1829

Comment: Haddock nowadays is more the subject of slapstick comedy routines and rude jokes than it is an article of food. The “Obs.” suggests that it might in fact have been just as disfavored in the early 19th century. One wonders if they may have been eaten primarily by the poor, or by residents of fishing communities where the higher-quality fish were sent off to markets where they brought a better rate of return.