In a shallow bowl or plate combine the flour and 1 T. of the Essence and stir to combine thoroughly. Quickly dredge the chicken breast halves in the seasoned flour mixture, shaking to remove excess.
Heat the oil in a large skillet over med-high heat until hot. Add 1 Tablespoon of butter and cook the chicken breasts until golden brown on both sides about 3 min per side. Transfer to a plate and set aside.
Add 1 T. of the remaining butter to the pan and add the mushrooms. Cook, stirring frequently, until mushrooms are golden brown around the edges and have given off their liquid. Add the Marsala wine and bring to a boil, scraping to remove any browned bits from the bottom of the pan. when the wine has reduced by half add the chicken stock and cook for 3 minute or until sauce has thickened.
Lower the heat to medium and return the chicken breasts to the pan and continue to cook until they are cooked through and the sauce has thickened about 5-6 minute.
Swirl in the remaining 2 T of butter, add salt and pepper to taste.