Preparation:
- Choose pork belly with a moderate amount of fat for a rich but not greasy filling. Clean the pork, remove the skin, and coarsely grind or chop (do not make it too fine).
- Use medium-sized river shrimp if possible. Remove the heads and tails (peel the shrimp if desired).
- Soak the wood ear mushrooms in water until they expand, then rinse and finely chop.
- Peel and clean the shallots and garlic. Slice the shallots thinly and mince the garlic.
- Wash and finely chop the scallions.

Reserve a small amount of shallots. Fry the rest in a pan with oil until golden, then remove and drain on paper towels.
- Add the chopped scallions to the hot oil, sauté briefly, then transfer to a separate bowl to make scallion oil.

Prepare the filling:
- Add the reserved shallots and minced garlic to a pan and sauté until fragrant. Add all the shrimp, pork, and chopped wood ear mushrooms. Stir-fry until cooked, then season with sugar, black pepper, and fish sauce to taste.

Make the dough for the wrappers:
- Place the tapioca starch and a pinch of salt in a large bowl and mix well.
- Add a little cooking oil, then gradually pour in hot water while stirring. When the dough cools slightly, knead until smooth and no longer sticky. The dough should be warm, soft, and pliable—not too wet or too dry.
- Divide the dough into 3-4 portions and cover to prevent drying while assembling the dumplings.

Shape the dumplings:
- Take one portion of dough, knead briefly to soften, then divide into small, equal pieces.
- Roll each piece into a ball, flatten with your palm, place some filling in the center, then fold the dough over and pinch the edges to seal so the filling stays inside. (You can shape them as you like.)

To serve: Arrange the dumplings on a plate, top with fried shallots and scallion oil, and serve with sweet and sour fish sauce. You can also enjoy them with Vietnamese pork sausage (chả lụa) or cinnamon pork sausage (chả quế) if desired.