Step 3
Using tongs, transfer the chicken to a plate and cover with aluminum foil to keep warm. Pour the sauce, including the garlic and mushrooms, into a large frying pan, add the butter, and bring to a simmer over medium heat. Whisk the water and cornstarch together in a small bowl until the cornstarch is dissolved, then pour into the simmering sauce. Cook until sauce thickens, 5 to 7 minutes.