Valois Sauce

Boil two gills of white wine with one gill of vinegar and add two tablespoonfuls of chopped shallots, let the liquid reduce thoroughly, then remove it from the fire, let partly cool and stir in six egg-yolks, beat them up with an egg-beater and finish the sauce with four ounces of fine fresh butter slowly incorporated; strain and after returning it to the saucepan stir into it two ounces more of butter and mix in one spoonful of chopped parsley, or replace half the parsley by chopped tarragon leaves if preferred.