Step 1

Start by making the broth. Heat up the premade broth or water to the steaming point, then add the chopped up smoked duck carcasses. If you are using water, feel free to add a chopped up onion, carrot and celery if you have them lying around. Let this steep at the steaming point -- don't let the broth simmer or boil -- for 4 hours. Then strain the broth. Put a sieve over a large bowl. Set a piece of paper towel in the sieve, then ladle the broth through this into the bowl. Keep the strained broth warm.

Step 2

While the stock is cooking, preheat the oven to 375°F. Toss the mushrooms with the melted duck fat or oil and salt them well. Set them in a roasting pan and grind some black pepper over them. Roast for 15 minutes and then turn off the heat. Let the mushrooms continue to roast as you do other things. They can sit in the oven for up to 3 hours.

Step 3

About 30 minutes before the broth is ready, pour off 2 cups and put that in a small pot. Add the rice and another cup of water and bring it to a boil. Cover the pot, lower the heat to its lowest setting and cook the rice. When the rice has absorbed all the water, about 15 minutes, turn off the heat but leave the lid on the pot.

Step 4

While the rice is cooking, fish out the legs and carcasses of the ducks and pick off as much meat as you can.

Step 5

To finish the soup, add the chopped mustard greens to the strained broth and let them cook until wilted, about 5 minutes. Put some shredded duck meat, rice and mushrooms in individual bowls and ladle over some of the broth and greens. Sprinkle chives on top and add lemon juice and black pepper to taste.