In a shallow bowl or plate combine the flour and Essence and stir to combine thoroughly

Quickly dredge the chicken breast halves in the seasoned flour mixture, shaking to remove any excess flour

Heat the oil in a large skillet over medium-high heat until very hot but not smoking

Add 1 tablespoon of the butter and cook the chicken breasts until golden brown on both sides, about 3 minutes per side

Transfer to a plate and set aside

Add 1 tablespoon 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 minutes, or until the sauce has thickened slightly

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 to 6 minutes

Swirl in the remaining 2 tablespoons of butter, add salt and pepper, to taste

Garnish with chopped chives and serve immediately