Mushroom sauce

Ingredients: Velute sauce, essence of mushrooms, butter.

Mix two dessert-spoonsful of essence of mushrooms with a cupful of veloute sauce, reduce, keep on stirring, and just before serving add an ounce of butter. This sauce can be made with essence of truffle[?], or game, or shallot.

Source: The Cook's Decameron: A Study In Taste, Containing Over Two Hundred Recipes For Italian Dishes from a project that puts out-of-copyright texts into the public domain. This is from a *very* old source, and reflects the cooking at the turn of the last century. Update as necessary.