How to Make It
In a large skillet, sauté the mushrooms in the oil over high heat for about 10 minutes, until softened and fragrant.
In a medium nonreactive saucepan, combine the wine, mushrooms, shallot and demiglace. Boil over high heat, stirring occasionally until reduced to 2 cups, about 10 minutes. (To make the sauce with pan juices, discard the fat from the sauté skillet, add the reduced wine mixture and boil for 30 seconds, scraping the bottom of the pan with a wooden spoon to dissolve the browned bits.) Off the heat, whisk in the butter to make a thickened sauce. Season with salt and pepper and serve.