Combine the pork skin and pork bones in a small pot, then cover with cold water.
260 g pork skin, 450 g pork bones, 950 ml water
Bring to a boil, drain, and immediately rinse the bones and skin to remove impurities. Rinse the pot and return everything to it. Add the water, ginger, scallions, and wine. Bring to a boil, then reduce the heat to low. Cover and simmer for 2 hours.
After 2 hours, turn off the heat, let the broth cool, and strain the liquid into a bowl. Once completely cool, cover and refrigerate overnight.
Optional: Blend half of the boiled pork skin with the broth until very smooth. Strain again if needed.
Dough:
In a mixing bowl, add the flour, then gradually stir in the warm water, 1 tablespoon at a time.
130 g all-purpose flour, 90 ml warm water
Knead the dough for 15 to 20 minutes until very pliable and smooth. Cover with a towel and let rest for 30 minutes.
Filling:
Place the ground pork in a food processor. Process for 30 to 60 seconds until it forms a paste.
450 g ground pork
In a mixing bowl, combine the pork with the remaining ingredients except the aspic. Whisk vigorously for about 2 minutes until extremely well combined and light and airy. Gently fold in the diced aspic; do not overmix.
Cover and refrigerate the filling until ready to assemble. If working right away, freeze for 15 minutes to firm up for easier assembly.
Folding:
Lightly dust a clean work surface with cornstarch. Roll the dough into a long cylinder about 1 inch in diameter.
Cut into equal pieces weighing about 11 grams each (about the size of gnocchi). Roll each piece into a round disc about 7.5 cm in diameter. Keep the wrappers covered with a damp cloth.
Prepare your bamboo steamer. Line with cheesecloth, napa cabbage leaves, or bamboo steamer liners (available at some Chinese restaurant supply stores). If using liners, brush them lightly with oil first.
Remove the filling. Working one at a time, place about 1 tablespoon of filling in the center of a wrapper. Pleat to form 12 to 20 folds and seal firmly at the top. If the filling becomes too soft or wet, freeze for an additional 15 minutes and continue.
Place the dumplings in the lined steamer basket, spaced about 5 cm apart.
Steaming:
In a metal steamer pot or wok, bring water to a boil.
Once boiling, set the bamboo steamer in the wok or steamer, cover, and steam over high heat for 8 minutes. Remove immediately and serve.
Notes
You can freeze the dumplings before cooking and steam them straight from frozen (about 15 minutes).