Pound the chicken breasts to an even thickness.
In a shallow dish, mix flour, salt, and pepper. Dredge the chicken in the flour, shaking off the excess.
Heat olive oil and butter in a large skillet over medium heat.
Sear the chicken for 4–5 minutes per side until golden brown. Remove from the skillet and set aside.
Add the mushrooms to the same skillet and cook for 5 minutes until browned.
Stir in the garlic and cook for another minute.
Pour in the Marsala wine and chicken broth. Bring to a simmer, scraping up any browned bits from the bottom of the skillet.
Cook for 5–7 minutes, letting the sauce reduce slightly.
Stir in the heavy cream (if using) and return the chicken to the skillet.
Simmer for 3–4 minutes, spooning the sauce over the chicken until fully coated and heated through.
Garnish with fresh parsley and serve hot with your choice of sides.