Mince an onion; fry it a yellow color, with butter, in a stew-pan; pour on a gill of vinegar; let it remain on the fire until a third of it is boiled away; then add a pint of gravy or stock, a bunch of parsley, two or three cloves, pepper, and salt; let it boil a minute; thicken it with a little butter and flour (_roux_); strain it, and remove any particles of fat.