Step 1

Preheat oven to 450°F. Place each piece of chicken between 2 sheets of wax paper, and pound to 1/8-inch thickness using a meat mallet or rolling pin. Sprinkle evenly with pepper and 1/2 teaspoon of the salt.

Step 2

Place flour in a shallow dish; dredge chicken lightly in flour, shaking off excess. Reserve 2 tablespoons of the flour, and set aside.

Step 3

Heat 2 tablespoons of the butter in a large nonstick skillet over medium. Cook chicken, in batches, until golden brown, 2 to 3 minutes per side (chicken might not be cooked through). Transfer chicken to a 13- x 9-inch baking dish coated with cooking spray, overlapping chicken if needed. Repeat procedure with remaining butter and chicken, adding 1 tablespoon butter to skillet before cooking each batch. Reserve drippings in skillet.

Step 4

Add 2 tablespoons of the butter and mushrooms to drippings in skillet; cook over medium, stirring occasionally, until tender and lightly browned, about 5 minutes. Sprinkle mushroom mixture evenly over chicken.

Step 5

Stir Marsala, stock, and remaining 1/2 teaspoon salt to drippings in skillet; bring to a simmer over medium-high. Simmer, stirring occasionally, until slightly reduced, about 8 minutes. Spoon about 1/3 of Marsala mixture (about 1/4 cup) over chicken.

Step 6

Combine cheeses in a small bowl, and sprinkle over chicken. Bake in preheated oven until chicken is cooked through and cheese is melted, about 6 minutes.

Step 7

Meanwhile, bring remaining Marsala mixture to a simmer over medium. Combine remaining 3 tablespoons butter and reserved 2 tablespoons flour in a small bowl until a paste forms. Add paste to Marsala sauce, and whisk until combined and thickened, about 2 minutes. Sprinkle chicken with parsley, and serve with Marsala sauce.