01 - Pat the chicken breasts dry and season both sides generously with salt and black pepper.
02 - Heat olive oil in a large skillet over medium-high heat. Add the chicken breasts and cook for 5–6 minutes per side until golden brown and cooked through to an internal temperature of 165°F. Remove from the skillet and set aside on a plate.
03 - Reduce heat to medium. Melt the butter in the same skillet, then add the onion and garlic. Sauté until fragrant, about 2 minutes. Add the sliced mushrooms and cook until softened and golden brown, approximately 5 minutes.
04 - Pour in the chicken broth, using a wooden spoon to scrape up any browned bits from the bottom of the skillet. Let the liquid simmer for 2 minutes to reduce slightly.
05 - Stir in the heavy cream and thyme. Simmer gently for 2–3 minutes, stirring occasionally, until the sauce thickens and coats the back of a spoon.
06 - Return the chicken breasts to the skillet. Spoon the mushroom cream sauce over the chicken and simmer for 2–3 minutes until the chicken is heated through and the flavors meld.
07 - Transfer to plates, spoon additional sauce over each portion, sprinkle with fresh chopped parsley, and serve immediately.