In a small bowl, combine marinade ingredients and whisk to blend.
Pour half of the marinade into the shallow dish (just big enough to hold all the duck legs in a single layer). Add the duck, moving it around the dish so the bottom sides get coated. Then pour the remaining marinade over the duck legs, making sure the top is completely coated. Cover with plastic wrap and pop in the fridge to steep for up to 3 hours. Marinate at least 30 minutes.
In a pestle and mortar, bash together the salt and pepper to a fine powder and set aside. You will be using it at the end of roasting.
Preheat the oven to 350 degrees. Shake the duck from the marinade (but save it!) and put them on a rack over a baking dish, skin-side up, and pour a few inches of water into the dish.
This is important as the duck will drip lots of fat and you don't want it swimming in it. The marinade will drip too, and it will BURN. You will never ever get your dish clean again if you don't have the water there. Put the duck in the oven for 1 1/2 hours.
Periodically brush a little of the reserved marinade over the duck. (Every 30 minutes or so)
Halfway through the cooking time, turn the legs over so that the cut side can be basted as well.
When there is only 10 mins cooking time left turn the legs again skin-side up, use up the last of the marinade (if there is any) and sprinkle the salt/pepper mix all over the skin and return to the oven.
Serves 4 or 2-3 if you have BIG eaters. Serve with a nice salad and bread or shred the meat and skin and serve with Mandarin Pancakes for a duck wrap. Accompaniments include scallions, cilantro and Hoisin Sauce.