To make the gelatin:

Rinse the chicken and ham under cold water, then pat dry with paper towels. Using a large knife or cleaver, chop the chicken wings and feet in half to expose the bone. Dice the pork belly and ham into large chunks. Combine with the water, scallion, ginger and garlic in a large stockpot. Bring the water to a boil and then reduce to a rolling simmer. Skim the foam and impurities that rise to the surface of the stock for a clearer broth. Cook the broth, uncovered, for 2½ hours. Strain the stock through a fine-mesh sieve or colander lined with a lint-free towel into a clean pot. Discard the solids (or pull the braised meat from the wing bones and chop and use for dumpling filling, stir-fry, salad, stew or sandwiches). Place the strained broth back on the burner.

To a tablespoon of soy sauce and two tablespoons of water, stir in the gelatin powder. Pour this mixture into a shallow baking dish. Pour the hot soup into the baking dish and use a fork to stir and whisk. Allow this mixture to cool enough to stop steaming, then cover and place in your refrigerator. Chill the stock for about 2 hours, until it is completely cold and set, like Jell-O. Using a fork, scrape up the gelatin and gently mash it to break it up into small pieces. You can also place in freezer to speed up chilling.

To make the filling:
Combine the ingredients in a bowl. Mix well. Stir in the soup gelatin until it is well distributed. Cover and refrigerate the filling until ready to use.

To make the dough:
Place the flour in a bowl and make a well in the center. Pour the boiling water and sesame oil into the center of the well and stir with a fork or pair of chopsticks until the dough begins to come together. You may need to add more water if it is dry, or if the dough is sticky, a touch more flour. Once the dough comes together, turn it out onto a lightly floured surface and knead lightly for 3 to 4 minutes, until it can be kneaded into a smooth ball.

Working on a lightly floured surface, roll the dough into a 2-inch (5-cm)-thick rope and divide the dough into 10 even pieces. Roll each piece into a 1-inch (2.5-cm)-thick rope and cut into 4 pieces, for a total of 40 pieces. Keep the dough covered in plastic wrap and refrigerate all but just the few pieces you are currently working with.

Using a small rolling pin, roll each piece of dough into a 4-inch (10-cm) circle about 1⁄16 inch (0.2 cm) thick.

To make the dumpling:
Add a heaping tablespoon (12 g) of filling to the center of the wrapper and wet the edges with a pastry brush or your finger. Begin to gather the edge of the wrapper and make tiny overlapping pleats, keeping the center of the dumpling as the focal point, until you have gathered all of the dough and the dumpling is formed. Gently pinch the pleats to seal the dumpling. Store on a lightly floured tray, covered with plastic wrap. Refrigerate the dumplings (as you go) or freeze as needed.

To steam the dumpling:
Arrange the dumplings at least 1½ inches (4 cm) apart in a dim sum steamer lined with blanched napa cabbage leaves or place a 3×3-inch piece of parchment paper under each dumpling. Place the dim sum basket over several inches of water in a wok (the water should reach just below the bottom tier of the first basket). Bring the water to a boil and steam the dumplings for 6 to 8 minutes, adding more water to the bottom pan as necessary. Serve hot with red vinegar dipping sauce.

To make the dipping sauce
Use a vegetable peeler to peel the ginger into very thin strips. Then, use a chef’s knife to thinly julienne the strips. Combine with the vinegar.