Begin by placing the white cabbage into a food processor and pulse until it reaches a finely chopped consistency. Sprinkle with half a teaspoon of salt, toss the cabbage gently to distribute the seasoning, and allow it to rest for 15 minutes. This step helps draw out excess moisture. Then transfer the cabbage onto a clean tea towel and squeeze thoroughly to remove as much liquid as possible, ensuring your filling won't be soggy. In a mixing bowl, combine the drained cabbage with grated carrot, finely chopped shiitake mushrooms, ground pork, minced garlic, grated ginger, soy sauce, sesame oil, and thinly sliced spring onions. Season with freshly ground black pepper. Using your hands, scrunch and mix the ingredients vigorously until evenly combined, creating a well-integrated, juicy filling. Next, prepare your rice paper sheets by briefly dipping each sheet for just a couple of seconds in a shallow dish of warm water. This softens them sufficiently without becoming too fragile. Lay each softened sheet on an oiled chopping board. Spoon one heaping tablespoon of the filling into the center of the sheet. Carefully fold the bottom edge over the filling, then bring down the top edge, folding in the sides to fully enclose the filling and shape a neat square parcel. If the rice paper feels delicate and flimsy, you can soak an additional sheet and wrap the dumpling again for extra sturdiness. Repeat this process with all the sheets and filling, placing the finished dumplings on an oiled plate to prevent sticking. Heat 75 ml of vegetable oil in a large non-stick frying pan, ensuring the oil fills no more than one-third of the pan's depth, over medium-high heat. Fry the dumplings for 3-5 minutes on one side until beautifully golden and crisp. Using a slotted spoon or spider, carefully turn them to brown the other sides. Cover the pan with a lid and cook for another 3-4 minutes to ensure the pork filling cooks through while retaining moisture. Remove the lid and fry for an additional 1-2 minutes to re-crisp the dumplings. Meanwhile, prepare the dipping sauce by combining 2 tablespoons of soy sauce, 2 tablespoons of rice vinegar, half a tablespoon of toasted sesame seeds, and thinly sliced spring onions in a small bowl. Serve the hot, crispy dumplings alongside the dipping sauce for a deliciously tangy accompaniment.