Step 1Place the cabbage in a large shallow bowl and sprinkle with 2 teaspoons kosher salt. Toss to mix thoroughly. Let stand 30 minutes, then drain completely and squeeze completely dry. Wipe the bowl clean and return the cabbage to it.
Step 2While the cabbage is softening, soak the mushrooms in boiling water until soft, about 20 minutes. Lift out of the water and drain well. Remove any stems and cut the caps into a fine dice. Add to the cabbage.
Step 3Add the pork to the bowl, then the sesame oil, green onions, chives, ginger, garlic, tamari, rice wine and a few grinds of black pepper. Using your hands or a wooden spoon, stir the mixture in one direction until all the ingredients are evenly incorporated. (This will take effort to get an even mix; don't give up too soon.) If you are not filling the dumplings right away, place a sheet of plastic wrap directly on the surface of the filling and refrigerate until needed.
Step 4To stuff the dumplings, mound about 2 teaspoons of the filling in the center of each wrapper and brush the edges lightly with water. Fold the wrapper in half, into a half-moon shape, then pinch it together at the center of the top edge. Pleat the edges of the wrapper to enclose the filling. Repeat with the remaining dumplings.
Step 5To pan-fry the dumplings, heat a 10-inch skillet with a lid over medium heat. Add 2 tablespoons oil and swirl the pan. When the oil is hot, place 8 to 10 dumplings in the pan, leaving room between each, and cook until the bottoms just start to brown, about 2 minutes. Add one-third cup water and reduce the heat to medium-low. Cover the pan and cook until the dumplings are soft on top, crisp on the bottom and the filling is firm, 5 to 7 minutes. Repeat with the remaining dumplings.
Step 6To steam the dumplings, use a steamer of your choice and bring 1 to 2 inches of water to a simmer (make sure the water level does not reach the bottom of the steamer). Lightly oil the steamer rack and place the dumplings on the rack about 1 inch apart (the dumplings will need to be cooked in batches). Place the steamer over the water and cover. Steam the dumplings until the filling is firm and the wrapper is slightly translucent, 10 to 15 minutes. Remove the steamer from the water and gently remove the dumplings to a warm place until all of the dumplings are cooked. Serve warm with a dipping sauce.