Wash the duck, dab dry and rub with salt and pepper. Close the belly opening with a wooden skewer. Tie the legs together over the rump. Coat the roaster with oil. Put the duck with the breast upwards.
Roast in the oven (electric cooker: 225 ° C/ convection oven: 200 ° C/ gas: level 4) for about 1 3/4 hours. After 15 minutes, pour 1/8 litre of hot water over it. Wash the oranges, grate dry, peel thinly, squeeze out the juice.
Cut the skin into fine strips, blanch in boiling water and drain. Turn down the oven temperature for the last 45 minutes (electric cooker: 175 °C/ circulating air: 150 °C/ gas: level 2) Remove the duck and keep it warm in the oven.
Degrease the gravy. Add chicken stock and orange marmalade, bring to the boil once. Mix sugar and vinegar, bring to the boil. Add orange and lemon juice. Sieve the sauce. Stir in butter flakes.
Season the sauce. Add orange liqueur. Garnish duck with orange peel and parsley.