01 - Sprinkle both sides of chicken breasts evenly with salt and black pepper.
02 - Heat olive oil in a large skillet over medium-high heat. Place the chicken breasts in the pan and sear for 4 to 5 minutes per side until golden and fully cooked. Transfer chicken to a plate and keep warm.
03 - Add butter to the same skillet. Once melted, add chopped onion and sauté for 2 minutes until softened. Add mushrooms and cook for 5 to 6 minutes until browned and tender.
04 - Stir in minced garlic and thyme. Cook for 1 minute until fragrant.
05 - Pour in chicken broth, bringing the mixture to a simmer while scraping up any browned bits from the pan.
06 - Lower the heat to medium-low. Stir in heavy cream and Parmesan cheese, blending until cheese melts and sauce thickens slightly, about 2 to 3 minutes.
07 - Return chicken breasts to the skillet. Spoon sauce and mushrooms over top. Simmer 3 to 4 minutes to warm chicken and meld flavors.
08 - Sprinkle fresh parsley over the dish before serving.