Pre-heat the oven to 375F.
Quarter the mushrooms.
In a small sauce pan, reduce the stock by half. This will save time and help keep the chicken hot later on.
Season the chicken with salt and pepper. Dust the chicken with flour.
Heat a large skillet over medium heat.
Film the pan with olive oil.
Place the chicken thighs in the pan, skin side down and saute for about 5 minutes, until golden on the skin side. Be careful not to burn the flour.
Remove the chicken and set aside.
Saute the mushrooms in the same skillet, using the oil in the pan.
Season the mushrooms and remove them from the skillet.
Return chicken and accumulated juices to the skillet. Nestle the thyme sprig between the thighs and place in the oven.
Roast until the chicken reaches an internal temperature of 165F.
Remove the chicken from the pan and deglaze with the marsala wine, scraping up any fond in the pan.
Add the stock and reduce slightly. Add the balsamic vinegar and cook a couple minutes more.
Return the mushrooms and mushroom liquor to the pan. Simmer until the mushrooms are heated through.
Off heat, stir in the butter, one tablespoon at a time.
To serve, place mushrooms on the plate. Place two chicken thighs overtop the mushrooms and drizzle the sauce around the chicken.