Remove the chicken from the oven. Arrange the carrots, celery, potatoes and onions around the chicken. In a 1-quart saucepan, heat the butter over low heat just until melted. (Or place the butter in a small microwavable bowl; cover with a microwavable paper towel and microwave on High 10 to 20 seconds or until melted.) Stir the thyme into the butter, then drizzle over the chicken and vegetables.