Robert Sauce

Chop two onions very fine, and fry them with a bit of butter the size of a large walnut, in a small stewpan, until they assume a light-brown colour; then add a wineglassful of vinegar and a good pinch of pepper, and boil these together for four minutes; next add a good tablespoonful of flour, or an ounce of thickening, No. 9, and half a pint of stock or water, and a bit of glaze; stir the sauce over the fire for twenty minutes, then add a tablespoonful of French mustard, one of Harvey, and a teaspoonful of anchovy; mix well together over the fire, and serve quite hot.