As the chicken thighs are baking, reduce skillet heat to medium.
Add to the skillet butter, garlic, and mushrooms. Using a wooden spoon, sautee until garlic and mushrooms have softened, about 5 minutes. Use the wooden spoon to scrape any drippings from the surface of the pan to make sure it gets incorporated into the mushroom sauce.
Add heavy whipping cream, water, thyme, basil, salt, and pepper.
Let sauce come up to a simmer, and stirring often, allow it to simmer until the sauce has reduced and has thickened, about 15 minutes.
Pour mushroom sauce over chicken thighs before serving.