Sauce For Boiled Cod, and Other Kinds of Fish

To 1 gill boiling water add as much milk; stir into this while
boiling 2 tablespoonfuls butter gradually, 1 tablespoonful flour
wet up with cold water; as it thickens the chopped yolk of 1 boiled
egg and 1 raw egg beaten light. Take directly from fire, season
with pepper, salt. a little chopped parsley and juice of one lemon,
and set covered in boiling water (but not over fire) 5 minutes,
stirring occasionally. Pour part of sauce over fish when dished;
the rest in a boat. Serve mashed potatoes with it.