Simmer the neck and giblets of duck in water to cover for about 1/2 hour. Chop giblets and discard neck. Melt butter and stir in flour. Add stock from giblets and orange marmalade and set aside. Season duck inside and out with salt and pepper and dredge lightly with flour. Put onion in cavity of duck. Peel one of the oranges and put in the cavity. Secure with skewers. Put onto a rack in a shallow roasting pan and cook for 30 minutes at 450° F.
Reduce heat to 350° F and pour marmalade gravy over the duck. Cook for 1 hour, basting occasionally. Remove duck from oven. Take most of fat from pan and make a gravy with the remaining pan drippings. Decorate with the remaining two oranges.
Servings: 4