Slice half an onion and fry it in a saucepan with half an ounce of butter and a teaspoonful of sugar until it is of a golden color, or about five minutes ; then moisten with half a glassful of white wine and half a pint of Espagnole sauce (No. 151). Boil for ten minutes ; then add a teaspoonful of dry English mustard, diluted in cold broth or gravy ; stir carefully, and finally rub through a hair sieve and serve.