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 to 6 minutes per side until golden brown and cooked through. Remove from the skillet and set aside on a plate.
03 - Reduce the heat to medium. Add the butter to the same skillet, then sauté the onion and garlic for about 2 minutes until fragrant. Add the sliced mushrooms and cook for approximately 5 minutes until softened and nicely browned.
04 - Pour in the chicken broth, scraping 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 the sauce for 2 to 3 minutes, stirring occasionally, until it thickens slightly and coats the back of a spoon.
06 - Place the chicken breasts back into the skillet. Spoon the sauce and mushrooms over the chicken and simmer for 2 to 3 minutes until everything is heated through and the flavors meld together.
07 - Sprinkle with chopped fresh parsley and serve immediately while hot.