Step 1Place the dried shiitake mushrooms in a small bowl and cover with very hot water. Weight the mushrooms so they stay submerged and set aside until the mushrooms are softened, about 20 minutes. Drain the mushrooms well and remove the stems. Mince the mushrooms and place them in a large bowl.
Step 2Heat a large skillet over medium-high heat until hot. Add the oil, then the cabbage. Sauté the cabbage, stirring frequently, until the cabbage wilts and is greatly reduced, 2 to 4 minutes. Remove from heat, then set aside to cool. When the cabbage is cool enough to handle, wring out the excess water and place in the bowl with the mushrooms.
Step 3To the mushrooms and cabbage, add the ground pork, ginger, chives, egg, garlic, pepper, soy sauce, sesame oil, fish sauce and wine, mixing well. To test, place a very small amount in a small nonstick pan and heat until the mixture is cooked through. Taste, adding salt to the mixture if desired. This makes about 2 cups filling.
Step 4Assemble the dumplings: Mix the cornstarch with the water in a small bowl. Put a heaping teaspoon of filling into each wrapper, and brush the edges of the wrapper with the cornstarch mixture. Fold the wrapper over into a crescent, forcing the air out of the dumpling as the edges are pressed together into folds. Try to create 8 folds, or pleats, on each dumpling for good luck. As the dumplings are formed, set them in a single layer on a baking sheet, making sure the dumplings do not touch. When finished, cover the baking sheet with plastic wrap and freeze. The dumplings can be frozen up to a few weeks.
Step 5To cook, bring a big pot of water to a boil. Add as many dumplings as desired, and boil until the wrappers are tender and the filling is firm; they will rise to the top when ready.
Step 1In a bowl, whisk together the vinegar, soy sauce, sugar, ginger and garlic, along with chili oil or sambal to taste, if desired. Serve with the dumplings.