As this is one of the best sauces ever made for boiled fish, asparagus, or cauliflower, I will give two receipts. The first is Dubois'; the second is from the Cooking - school in New York. None should call themselves cooks unless they know how to make the sauce Hollandaise, and simple enough it is.
1st. "Pour four table-spoonfuls of good vinegar into a small stew-pan, and add some pepper-corns and salt; let the liquid boil until it is reduced to half; let it cool; then add to it the well-beaten yolks of four or five eggs, also four ounces (size of an egg) of good butter, more salt, if necessary, and a very little nutmeg. Set the stew-pan on a very slow fire, and stir the liquid until it is about as thick as cream; immediately remove it. Now put this stew-pan or cup into another pan containing a little warm water kept at the side of the fire. Work the sauce briskly with a spoon, or with a little whisk, so as to get it frothy, but adding little bits of butter, in all about three ounces" (I would say the size of half an egg). "When the sauce has become light and smooth, it is ready for use."
2d. "Put a piece of butter the size of a pigeon's egg into a saucepan, and when it bubbles stir in with an egg-whisk an even table-spoonful of flour; let it continue to bubble until the flour is thoroughly cooked, when stir in half a pint of boiling water, or, better, of veal stock; when it boils, take it from the fire, and stir into it gradually the beaten yolks of four eggs; return the sauce to the fire for a minute, to set the eggs, without allowing it to boil; again remove the sauce, stir in the juice of half a small lemon, and fresh butter the size of a walnut, cut into small pieces, to facilitate its melting, and stir all well with the whisk."