1 (1½ pounds) head Savoy cabbage
8 large king oyster mushrooms (about 1/2 pound), cut into 3/8 inch cubes
2 duck legs (about 1¼ pounds total), skins on and bones removed
3 tablespoons orange juice (from about 1 orange)
3 tablespoons soy
2 teaspoons mirin
2 scallions, finely sliced
1 tablespoon minced ginger (from about a 1½-inch piece)
1 tablespoon minced garlic (from about 2 medium garlic cloves)
1 tablespoon orange zest (from about 1 large navel orange)
Bring a large pot of salted water to a boil. Fill a large bowl of ice and water; set aside. Carefully remove 8 to 10 outer green leaves of the cabbage without ripping. Trim out the spine and cut into 2 equal halves.
Once the water is boiling, boil the trimmed cabbage leaves until just tender, about 1 minute. Immediately drain and transfer the leaves to the bowl of ice water to “shock” or stop the cooking process. Place on paper towels to dry.
Quarter and core the remaining cabbage round. Cut 2 cups worth of finely shredded cabbage.
Trim the bottoms off the mushrooms and discard. Cut about 1 to 1½ inch off the top of the mushrooms and set aside for garnish. Cut the center of the mushrooms into 3/8-inch dice. You should have about 1 cup diced mushrooms.
Heat a large skillet over high heat. Add enough canola oil to coat the bottom of the pan. Add the mushrooms and sauté until golden brown about 2-3 minutes. Season with salt and pepper Add the shredded cabbage and until wilted and starting to brown on the edges, another 5 minutes. Taste and season with salt and pepper. Set aside on a small baking sheet to cool. Set aside on a small baking sheet lined with paper towel to cool.
Remove the duck meat from the bones (or ask the butcher to do it for you). To do so, first remove excess fat and cartilage that runs beyond the meat. Follow your knife along the bones of the duck leg, cutting the meat as you go to release it from the bone until the entire leg has been deboned. Remove sinew when possible. Place in a medium bowl and set in the freezer to chill or place the bowl over a bowl of ice. You can also place the food processor blade in the ice to ensure that all of the elements of the dumpling stuffing are cold when grinding in the food processor.
Once well chilled, quickly place in the food processor and pulse, scraping down the sides as needed, until meat is broken down and begins to look creamy, about 15 (1-second) pulses. Note: if the duck is not cold enough, the blade will not be able to cut through the fat and the meat.
Add orange juice, soy sauce, and mirin, and process for about 5 to 10 seconds until incorporated.
Scrape the contents into a medium-sized bowl and set on top of a larger bowl filled with ice. Add scallions, garlic, ginger and orange zest. Stir until combined. Mix in the cooled mushrooms and cabbage. Chill again in the refrigerator until ready to make dumplings.
Cut plastic wrap into 10 inch squares.
Lay a cabbage leaf on a piece of plastic wrap and with a large spoon place about 1 tablespoon of the filling in the middle of the cabbage. Pick up the corners of the plastic wrap and bring them together, making sure the cabbage is folded over the filling. Press the wrap tightly around the cabbage to form a ball, while twisting the length of the plastic wrap until completely twisted. Tie into a knot close to the ball and trim excess plastic wrap. Repeat with remaining cabbage leaves and stuffing.
Fill a large pot that holds a large steam basket snuggly with 3 inches of water and bring to a low steady boil. *Place steamer basket over the pot and place cabbage rolls in the basket. Steam until the dumpling pouches are filled with juices, about 7 minutes.
Remove dumplings and let cool slightly. Cut dumplings open over a plate to catch the juices. Remove plastic wrap and serve hot with juices. Note: if you do not have a steamer basket, you could steam the dumplings in a shallow sauté pan with water.