1) Preheat the oven.
2) Sprinkle salt over the duck pieces.
3) In a raosting pan, arrange the duck pieces.
4) Place the tin on rack of preheated oven and cook for at least 30 minutes.
5) In a small pan, mix the arrowroot with orange juice.
6) Boil the liquid and add grapes.
7) On a warm serving dish, place the roasted duvk and pour the sauce over it.
8) Serve with garnish of watercress and orange slices.