In a stock pot, combine the Espagnole sauce and brown stock together. Bring up to a boil and reduce to a simmer. Skim the liquid often for impurities. Add the bouquet garni and continue to simmer. Simmer the sauce until it reduces by half. Season with salt and pepper. Add the Madeira and strain through a China Cap. Spoon a couple of ladles of the sauce in the Sauteed mushroom mixture. Bring the sauce up to a simmer. Lay the fillet in the center of the plate. Arrange the potatoes around the fillet. Spoon the sauce over the fillet. Garnish with long chives and chopped parsley.
Recipe courtesy of Emeril Lagasse