01 - Pat the chicken breasts dry with paper towels. Season both sides generously with salt and freshly ground 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 to an internal temperature of 165°F. Remove from the skillet and set aside on a plate.
03 - Reduce the heat to medium. Add the butter to the same skillet. Sauté the chopped onion and minced 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 dried thyme. Simmer the sauce for 2 to 3 minutes, stirring occasionally, until it thickens slightly and coats the back of a spoon.
06 - Return the chicken breasts to the skillet. Spoon the mushroom sauce over the chicken and simmer for 2 to 3 minutes until everything is heated through and the flavors meld together.
07 - Sprinkle with freshly chopped parsley and serve immediately while hot.