Remove the dough from the bag, turning the bag inside out if the dough is sticky. Put the dough on a lightly floured surface and cut it in half. Put half back in the bag, squeezing out the air and sealing it closed to prevent drying.
Roll the dough into a 1-inch-thick log and cut into 16 pieces (cut in half, then cut each half in half, and so on to create pieces that are even in size. The tapered end pieces should be cut slightly larger). If your pieces are oval, stand them on one of the cut ends and gently squeeze with your fingers to make them round, like a scallop. Take each piece of dough and press each cut end in flour, lightly pressing the dough to about ¼ inch thick and set aside.
Next, flatten each dough disk into a thin circle, about ⅛ inch thick, either with a tortilla press (lined with plastic wrap), or with a heavy flat-bottomed object like a frying pan (also lined with plastic). Alternatively, I used a dowel (which is a good lightweight rolling pin alternative for fast and flexible dumpling making) to lightly roll out each disc into an ⅛ inch thick circle.
To finish the wrappers, place wrappers one at a time on your work surface, and flour only if sticky. Imagine a quarter-size circle in the center of the dough. This is what the Chinese call the “belly” of the wrapper. You want to create a wrapper that is larger than its current size, but still retaining a thick “belly” in the center. This ensures an even distribution of dough when the dumpling is sealed. Use the rolling pin to apply pressure to the outer ½-to-¾-inch border of the wrapper. Roll the rolling pin in short downward strokes with one hand while the other hand turns the wrapper in the opposite direction. Aim for wrappers that are about 3 ¼ inches in diameter. When a batch of wrappers is formed, fill them before making wrappers out of the other portion of dough.
Line a baking sheet with parchment paper (if planning to refrigerate dumplings for several hours, also dust with flour to prevent sticking). Hold a wrapper in a slightly cupped hand and scoop about 1 tablespoon of filling slightly off-center toward the upper half of the wrapper, pressing and shaping it into a flat mound and keeping a ½-to-¾-inch border on all sides.
To make “pea pod” shapes, fold the edge of the wrapper closest to you to meet the top edge and pinch together to seal well. Place on your work surface and press gently to steady the dumpling and make it sit flat. Fold the sealed edges of the dumpling to make a series of pleats from one end to the other. Place finished dumplings on the prepared baking sheet. Repeat with the remaining wrappers and dough, spacing out dumplings about ½ inch apart. Keep the finished dumplings covered with a dry kitchen towel.
When all the dumplings are assembled, they can be covered with plastic wrap and refrigerated for several hours and can be cooked straight from the refrigerator. For longer storage, freeze them on their baking sheet until hard (about 1 hour), transfer to a zip-top freezer bag, pressing out excess air before sealing, and frozen for up to 1 month. To cook after freezing, partially thaw, using your finger to smooth over any cracks that may have formed during freezing, before cooking.