Preheat the oven to 475°. In a large enameled cast-iron casserole, heat the oil over moderately high heat. Season the chicken inside and out with salt and pepper and tie the legs together. Set the chicken in the casserole on 1 breast, cover and roast in the oven for 30 minutes. Carefully turn the chicken onto its other breast, cover and roast for 20 minutes. Turn the bird on its back, cover and roast for 20 minutes longer, or until the juices run clear when a thigh is pierced. Transfer the chicken to a platter, cover, and keep warm.