For the duck:

1. The day before serving, stuff the duck with the onion and celery. Place the duck, breast side up, in a large soup pot with enough water to half cover it. Add the ginger and bring to a boil. Cover and reduce the heat so that it simmers very gently for 45 minutes.
2. After 45 minutes, turn the duck over. Add the sugar, soy sauce and salt. Continue simmering for another 45 minutes. Turn duck once again and simmer until tender and almost falling apart, about another 45 minutes. Turn off the heat and when cool enough, carefully remove duck from pot and place in a roasting pan. Cover and refrigerate until the next day.
   Be very gentle with the duck, it will be close to, if not, falling apart.
3. Strain the broth into a container and chill overnight. A layer of fat will form on top. Scrape off and reserve. Reserve the broth separately.
4. About 2 hours before serving, bring duck to room temperature in roasting pan. Preheat oven to 350°. Add the sherry and 1 cup of the defatted duck broth to the roasting pan and place in the oven. Roast uncovered for 45 minutes to 1 hour, basting occasionally with the juices from the pan. The duck is done when it is heated through and the skin is crisp and chestnut brown.
5. Transfer the duck to a serving platter and garnish with watercress.
   Use the watercress to hide any bits that are falling off.

For the rice:

1. While the duck is crisping, melt the duck fat in a medium pot over medium heat. Add the onion and garlic and sauté until the onion is translucent. Add the rice and cook until lightly toasted. Add the broth and bring to a boil. Reduce the heat to as low as possible, cover and simmer until the rice is tender, 16 to 20 minutes. Fluff the rice and season to taste with salt and pepper. Cover to keep warm until serving time.