If making wrappers: combine 1 cup all-purpose flour with 1/4 cup plus 1 teaspoon water and knead until smooth and not sticky; cover with a damp cloth and rest 30 minutes. On a floured surface, roll into a long cylinder, divide, and roll each piece into a wrapper about 4 inches (10 cm) in diameter; set aside. Or use store-bought round dumpling wrappers.
Prepare the filling: in a mixing bowl combine ground chicken thighs, finely sliced Napa cabbage (squeezed of excess liquid), grated ginger, chopped scallion, soy sauce, sesame oil, ground white pepper, and a pinch of salt; mix thoroughly until well combined.
To assemble: place one wrapper in your palm and put about 1 teaspoon of filling in the center. Moisten the wrapper edge with a little water, fold to form a half-moon, and press the edges to seal tightly; arrange finished dumplings on a parchment-lined plate. Repeat with remaining wrappers and filling.
Boil: bring a pot of water to a rolling boil, gently add dumplings, and cook until they float and are cooked through, a few minutes; scoop out with a strainer and transfer to a plate. Cook remaining dumplings in batches.
Pan-fry: heat a skillet with oil over medium heat. Arrange about 8 boiled dumplings in the skillet and fry until the bottoms are light brown, about 2–3 minutes. Turn and brown the other sides, adding more oil as needed, until all dumplings are golden and crisp.
Serve: plate the dumplings warm with Chinese black vinegar or ponzu and optional chili oil for dipping.
