From: The Thorough Good Cook

Sauces: 46. Oyster

Preserve the liquor of your oysters as you open them, and strain it through a fine sieve. Wash the oysters very clean, and take off the beards. Put them into a stew-pan, and pour the liquor over them. Add a large spoonful of anchovy liquor, half a lemon, two blades of mace, and thicken with butter rolled in flour. Then put in half a pound of butter, and boil it up till the butter is melted. Now take out the mace and lemon, and squeeze the lemon juice into the sauce. Give it a boil, stirring it all the time, and pour it into your sauce-boat.
Noder's Note: This sauce bears no relation to the Chinese sauce of the same name. This is a western sauce.