Leave the duck legs for simmering ina large boiling water pan for around 1.5 hours.
To ready the sauce, fry peeled, chopped onions in 2 oz ( 50 g) of the butter for about six minutes or soft. Add grated and peeled ginger with cardamom seeds and the sugar from one pod. Prepare until the color of the mixture turns golden brown.
Add the boil and stock until the volume is decreased by half. Reduce by half again till syrup-like after adding the white wine and dry ginger. Add salt and freshly ground pepper, and fresh orange juice to taste.
Stir in 1 oz (25 g) of the butter into the sauce at boiling point. Separate the onions from the mix and combine with the rest of the butter. Keep it aside.
Remove water from the duck and put it over a rack or a roasting tin. Carefully brush the duck with oil and spray with salt and the remaining cardamom seeds.
Roast until the skin is crisp. It takes about 30 minutes at gas mark 8. (450 F, 230 degrees centigrade). Add the onion and reheated butter and serve the food with heated cardamom sauce. Garnish with coriander and serve hot.