Whisk together the chicken broth and sour cream. Set aside.
Combine flour and Creole seasoning in a Ziploc bag. Set aside.
Trim chicken breasts of all fat. Horizontally slice chicken breasts in half. Place between plastic wrap and pound to ¼-inch thick. If the pieces are large, cut in half.
Combine the flour and Creole seasoning in a Ziploc bag. Add the chicken pieces; shake to coat.
Heat the oil in a large skillet over medium heat. Add the coated chicken pieces in batches; cook tuntil golden brown on both sides, about three minutes per side. Transfer to a plate and set aside.
Add the mushrooms to skillet; cook over high heat, stirring frequently, until the 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 broth/sour cream mixture and cook for 3 minute, or until the sauce has thickened slightly. (See Tip 4)
Lower the heat to medium and return the chicken breasts to the pan. Continue to cook until the chicken breasts are cooked through and the sauce has thickened, about 5 to 6 minutes. Season to taste with salt and pepper. If desired, garnish with minced parsley or chopped chives and serve immediately. Yield: 6 servings.