Remove the excess fat from the cavity of the duckling.
To prepare the dressing, heat the butter in a 11" frying pan.
Add the walnuts and saute over moderate heat for five minutes.
Add and saute the onion.
Remove from the heat and stir in all the remaining stuffing ingredients except the softened butter.
Fill the duck cavity and truss securely.
Prick the duck skin with a fork in many places and rub the skin with the remaining softened butter.
Place the duck on a rack in a large au gratin dish.
Roast uncovered in a preheated 350° oven for 1 1/4 hours or until an internal temperature of 190° is reached.
Allow the duck to rest for 20 minutes before carving.