Pork Dumplings with Aged Black Vinegar

In a medium bowl, mix the ground pork with the wine, sugar, salt and pepper. Dust a rimmed baking sheet with cornstarch. Moisten the edge of a gyoza wrapper with water and place 1 teaspoon of the pork filling in the center. Bring the sides up and over the filling, pleating the wrapper and twisting it at the top. Set the dumpling on the baking sheet. Repeat with the remaining filling and wrappers. In each of 2 large skillets, warm 2 tablespoons of the vegetable oil over low heat. Add the dumplings to the skillets, increase the heat to high and fry until browned on the bottom, about 2 minutes. Pour 1/2 cup of the water into each skillet, cover and reduce the heat to moderate. Cook until the water has evaporated and the dumplings are tender on top and sizzling and crisp on the bottom, about 7 minutes. Meanwhile, in a small bowl, combine the vinegar and soy sauce and pour into individual dipping bowls. Arrange the apple slices on a platter or plates. Set the dumplings on the apple slices and serve at once, with the dipping sauce.