How to Make It
Make the filling In a small bowl, cover the mushrooms by 1 inch with boiling water. Let stand until tender, about 30 minutes. Drain well and finely chop (you should have 1/3 cup).
In a medium bowl, mix the shrimp with the mushrooms, chives, oil, sugar, salt and cornstarch. Let stand for 10 minutes.
Meanwhile, make the dough In a large bowl, stir the wheat starch and 1/2 cup of cornstarch with the boiling water until the dough comes together; let cool slightly. Lightly dust a work surface with cornstarch and turn the dough out onto it, then knead until smooth, about 2 minutes. Wrap the dough in plastic and let rest for 15 minutes at room temperature. Cut the dough into 2 equal pieces. Roll each piece into a 1-inch-thick log (12 inches long) and cut each log into twelve 1-inch-thick slices. Using a lightly cornstarch-dusted rolling pin, roll out each piece of dough to a 3 1/2-inch round. Arrange the wrappers on a cornstarch-dusted baking sheet (it’s OK if they overlap slightly) and keep covered with plastic wrap while you prepare the rest.
Spoon 1 tablespoon of the filling in the center of each wrapper. Fold the dough up and over the filling to form a half-moon and pleat to seal the dumpling completely. Repeat with the remaining filling and wrappers.
Line a large steamer basket with parchment paper and lightly grease or spray the paper with oil. Set the basket in a pot of boiling water. In 2 batches, steam the dumplings until the wrappers turn transparent and the filling is firm to the touch, 8 to 10 minutes. Serve with soy sauce for dipping.
Wheat starch is a key ingredient to making the translucent wrappers for many dumplings. Look for it at Asian markets and on amazon.com.