Sauce Robert.
Melt an ounce of butter, and put to it half an ounce of onion, mixed fine; turn it with a wooden spoon till it takes a light brown colour; stir into it a table-spoonful of mushroom ketchup, and the same quantity of port wine. Add half a pint of broth, a quarter of a tea-spoonful of pepper, and the same of salt; give them a boil; add a tea-spoonful of mustard, the juice of half a lemon, and one or two tea-spoonfuls of vinegar or tarragon.