Take a flat-bottomed pan and ensure it is clean and dry. Pour an appropriate amount of cooking oil into the pan, swirling it to evenly coat the bottom. Arrange the dumplings with some space between them to prevent sticking. Set the heat to low and fry the dumplings slowly over low heat.

Keep an eye on the bottom of the dumplings. As time passes, the bottom of the dumplings will begin to change color, and when they turn a delicious golden brown, the initial frying is done. At this point, the bottom of the dumplings is firm, and they should have a crispy texture.

In a small bowl, add 20g of all-purpose flour. Slowly pour in 200g of water, stirring with chopsticks or a spoon until the flour is fully dissolved and the mixture is smooth and lump-free. Set aside.

Slowly pour the prepared flour-water mixture around the edges of the pan, letting it evenly spread around the dumplings. The flour-water should cover about one-third of the height of the dumplings. This height ensures that the dumplings will absorb enough moisture during frying to cook through, while also allowing the flour-water to form a thin, crispy "skirt" at the bottom of the pan.

Immediately cover the pan with a lid and turn the heat to medium-low. During this steaming process, you'll hear a sizzling sound as the flour-water evaporates and solidifies.

Continue to monitor the pan. When the sizzling sound starts to fade, lift the lid and check. The flour-water should have evaporated, and a golden, crispy layer should have formed at the bottom of the pan. At this point, the dumplings are almost done. Turn off the heat, and sprinkle chopped scallions and toasted sesame seeds evenly over the dumplings.

Grab a plate large enough to cover the entire pan. Gently place the plate over the dumplings, then press down lightly with one hand while holding the pan handle with the other. Quickly flip the pan onto the plate, and then slowly lift the pan. The dumplings will come off easily with the crispy layer intact, transferring smoothly to the plate.