No. 28 Sauce Robert.
Peel and cut up four middling-sized onions into very small dice, put them into a stewpan with two ounces of butter, stir them over a moderate fire until rather brown; then add two tablespoonfuls of common vinegar, let it boil; then add a pint of brown sauce (No. 1), with half a pint of consommé (No. 134), let it simmer at the corner of the stove ten minutes; skim it well, then stir it over a sharp fire, reducing it until rather thick; finish it with two tablespoonfuls of French mustard, a little sugar, and salt, if required.