Shanghai's soup dumplings, whose broth starts as a solid - a wobbly pork-skin aspic diced cold into the filling, which melts back into liquid the instant steam hits it, trapped inside a wrapper pleated at least 18 times around the top.
1.Simmer the pork skin with the water, ginger, and scallions for 2-3 hours until the liquid reduces and turns rich with released collagen.
2.Strain the liquid and refrigerate until it sets into a wobbly aspic, then dice it into small cubes.
3.Mix the ground pork with the soy sauce, wine, sesame oil, sugar, grated ginger, white pepper, and chopped scallion, then fold in the diced cold aspic just before wrapping so it stays solid rather than melting into the filling.
4.Make the dough with the flour and warm water, knead until smooth, rest for 20 minutes, then roll into a log and cut into small pieces, rolling each into a thin circle - thinner at the edges and thicker in the center to support the weight of the soup.
Place a spoonful of filling with several aspic cubes in the center of each wrapper, then pleat the edges around while rotating the dumpling, aiming for at least 18 pleats gathered at the top and twisted to seal.
6.Steam over high heat for 8-10 minutes - the moment the dumplings hit the steam, the cold aspic melts back into hot broth trapped inside the dough.
7.Serve immediately with black vinegar and julienned ginger, lifting each dumpling carefully by the top knot to avoid tearing the delicate skin, and biting a small hole to sip the broth before eating the rest.