Begin by seasoning both sides of the chicken breasts with salt and freshly ground black pepper. Dredge each piece in all-purpose flour, ensuring an even, light coating. Shake off any excess flour.

In a large skillet over medium-high heat, warm the olive oil. Add the floured chicken breasts to the skillet. Cook for about 4-5 minutes on each side, or until they develop a golden-brown crust and are cooked through. Once done, transfer the chicken to a plate and set aside.

In the same skillet, add the sliced mushrooms. Sauté for approximately 5 minutes until they become tender and release their juices. Add the minced garlic and cook for an additional minute, stirring frequently to prevent burning.

To create the sauce, pour the chicken broth into the skillet, scraping up any browned bits from the bottom of the pan. Add the white grape juice, sherry vinegar, and vanilla extract. Stir the mixture well to combine all the flavors.

Allow the sauce to come to a gentle simmer. Let it cook for about 5 minutes, reducing slightly to concentrate the flavors. Stir in the heavy cream and unsalted butter, continuing to cook for another 2-3 minutes until the sauce thickens to your desired consistency. Season with additional salt and pepper if needed.

Return the cooked chicken breasts to the skillet, nestling them into the mushroom sauce. Spoon the sauce over the chicken to ensure each piece is well-coated. Let the chicken warm through in the sauce for about 2 minutes.

Transfer the Chicken Marsala to serving plates. Garnish with freshly chopped parsley for a burst of color and freshness. Serve hot alongside your preferred side dishes.