Mushroom sauce

Ingredients: Veloute 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.