Prepare the Soup Aspic: Place the pork skin and bones in a large stockpot and cover with cold water. Bring to a boil and cook for 5 minutes to clean them. Drain and rinse the skin and bones thoroughly under cold water. Return them to the clean pot with 1.5 litres of fresh water, the chopped spring onions, ginger slices, and Shaoxing wine.

Simmer the Broth: Bring the pot to a boil, then reduce the heat to a low simmer. Skim off any scum that rises to the surface. Partially cover and let it simmer very gently for at least 2-3 hours. The liquid should reduce by about half and feel slightly sticky between your fingers.

Strain and Chill: Strain the broth through a fine-mesh sieve into a shallow dish or container, discarding the solids. Let it cool to room temperature, then cover and refrigerate for at least 3 hours, or preferably overnight, until it's completely firm and gelatinous.

Make the Filling: Once the aspic is set, remove it from the container and finely mince it into tiny pieces. In a large bowl, combine the minced pork, light soy sauce, dark soy sauce, Shaoxing wine, sesame oil, sugar, and white pepper. Mix vigorously in one direction with chopsticks or a spatula until the mixture becomes sticky and paste-like.

Combine Filling and Aspic: Gently fold the minced aspic, grated ginger, and chopped spring onions into the pork mixture. Try not to overmix at this stage. I find it helps to chill the completed filling for 30 minutes; it makes it less sticky and much easier to handle when wrapping.

Assemble the Dumplings: Place about 1 tablespoon of filling in the centre of a dumpling wrapper. Using your fingers, carefully pleat the edge of the wrapper around in a circle, gathering it at the top. Aim for 16-18 pleats for a classic look. Pinch the top firmly to seal the dumpling completely. Place the finished dumpling on a tray lined with parchment paper. Repeat with the remaining filling and wrappers.

Prepare the Steamer: Line a bamboo steamer basket with perforated parchment paper or large cabbage leaves. This prevents the delicate dumplings from sticking.

Steam to Perfection: Arrange the dumplings in the prepared steamer, leaving at least 2cm of space between each one to allow for expansion. Bring water to a boil in a wok or pot that the steamer can sit over. Place the steamer over the boiling water, cover, and steam for 8-10 minutes, until the wrappers are translucent and the filling is cooked through.

Prepare the Dipping Sauce & Serve: While the dumplings steam, mix the black vinegar, soy sauce, and julienned ginger in a small bowl. Serve the dumplings immediately, straight from the steamer, with the dipping sauce on the side.