Shanghai soup dumplings whose 'soup' is actually a savory pork gelatin, solidified from a pork-skin stock and chilled until firm, then diced and folded into the filling so it melts back into broth as the dumplings steam - folding in solid gelatin instead of trying to spoon in liquid broth is the real trick that keeps the soup sealed inside during pleating.
1.Blanch the pork skin in boiling water for 5 minutes, then scrape off any remaining fat and hair and rinse well.
2.Simmer the cleaned pork skin with the water, ginger slices, and scallions for 2-3 hours, until the liquid has reduced by about half and turned slightly syrupy - this long simmer is what breaks the skin's collagen down into natural gelatin.
3.Strain the stock, discarding the solids, season lightly with salt, then pour into a shallow dish and refrigerate for at least 3 hours, until firmly set into a jelly.
4.Once set, dice the pork jelly into small cubes. Mix the ground pork with the soy sauce, shaoxing wine, sesame oil, sugar, minced ginger, and minced scallion until well combined, then fold in the diced pork jelly - folding in solid, chilled jelly rather than trying to add liquid broth is what keeps the soup sealed inside the dumpling until it steams.
5.Place a spoonful of filling in the center of each dumpling wrapper. Pleat the edges around the filling, working in one direction and overlapping each pleat slightly, aiming for 12-18 pleats, then twist and pinch the top to seal completely.
6.Line a steamer basket with parchment paper or cabbage leaves, arrange the dumplings with space between them, and steam over boiling water for 8-10 minutes, until the wrappers are translucent.
7.Serve immediately, very carefully - bite a small opening in the wrapper first to let the hot soup cool slightly, then eat with black vinegar and julienned ginger.