Roast the chicken for one hour at 325 degrees F. Once roasted, cut the chicken into pieces and place in a large baking dish. Pour the cognac over the chicken and let marinate for at least 12 hours, turning the chicken every six hours. Once the chicken has marinated, place the butter, lard, onions, chicken (including the marinade), salt and pepper in a large heavy pot over medium heat. Cover and let cook for a maximum of one hour. To plate: Place chicken on a serving dish and garnish with parsley, if desired.