01 - Place chicken breasts between plastic wrap sheets. Pound gently to 1/2-inch thickness. Season both sides with salt and pepper, then dredge in flour, shaking off excess.
02 - Heat 2 tablespoons olive oil in a large skillet over medium-high heat. Cook chicken 3–4 minutes per side until golden brown and cooked through. Transfer to plate and tent with foil.
03 - Add remaining olive oil and butter to skillet. Cook mushrooms 5–6 minutes, stirring occasionally, until browned and liquid has evaporated.
04 - Add garlic and sauté 30 seconds until fragrant.
05 - Pour in Marsala wine, scraping up browned bits from bottom of pan. Simmer 2–3 minutes to reduce slightly.
06 - Add chicken broth and return chicken breasts with juices to skillet. Simmer 7–8 minutes, turning chicken once, until sauce thickens slightly.
07 - Stir in heavy cream if using and simmer 1 minute.
08 - Remove from heat. Sprinkle with chopped parsley and serve immediately with lemon wedges if desired.