3 boneless, skinless chicken breasts (about 1 3/4 lb.), halved lengthwise
¼ teaspoon black pepper
1 teaspoon kosher salt, divided
½ cup (about 2 1/8 oz.) all-purpose flour
½ cup (4 oz.) unsalted butter, divided, plus more if needed
Cooking spray
8 ounces cremini mushrooms, thickly sliced (about 1 1/2 cups)
¾ cup Marsala
½ cup chicken stock
1/2 cup Fontina or mozzarella cheese, shredded (about 1/2 cup)
1/2 cup Parmesan cheese, grated
Chopped fresh flat-leaf parsley, for garnish
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.
Place flour in a shallow dish; dredge the chicken lightly in the flour, shaking off the excess. Reserve 2 tablespoons of the flour, and set aside.
Heat 2 tablespoons of the butter in a large nonstick skillet over medium.
Cook chicken, in batches, until it’s golden brown, 2 to 3 minutes per side (chicken might not be cooked through).
Transfer the 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 the drippings in skillet.
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.
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.
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.
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.
Turkey breast may be substituted for chicken. Instead of Marsala wine, 3/4 cup dry white wine may be used.