Step 1

Stir together flour and salt in a large heatproof bowl. While stirring constantly with a fork or chopsticks, pour boiling water into flour mixture until shaggy pieces of dough form. Knead in bowl until flour absorbs all water, about 2 minutes. Continue kneading until smooth, about 3 minutes. Shape into a ball, and cover with a damp cloth. Let rest at room temperature at least 1 hour or up to 2 hours.

Step 2

Pulse chopped cabbage in a food processor until finely chopped, 4 to 6 pulses. Transfer cabbage to a clean kitchen towel, and squeeze firmly over sink to remove any excess liquid. Transfer cabbage to a medium bowl; stir in pork, scallions, chives, soy sauce, garlic, ginger, and sesame oil until well combined. Chill, covered, until ready to use.

Step 3

Lightly dust 2 baking sheets with cornstarch; set aside. Divide wrapper dough evenly into 4 portions. Place 1 dough portion on a clean work surface; cover remaining portions with a damp cloth. Knead dough portion until smooth, about 15 seconds, if needed. Roll dough portion into a 10-inch-long rope (about 3/4 inch thick). Cut rope crosswise into 10 (1-inch-long) pieces (about 1/4 ounce each). Cover dough pieces with a damp paper towel. Working with 1 dough piece at a time, roll into a ball with your hands. Place rolled dough ball on work surface, and, using the bottom of a measuring cup, push down to flatten into a circle. Lightly dust both sides of dough circle with flour; using a dowel rolling pin, roll into a 3 1/2-inch circle. (If desired, you can trim using a 3 1/2-inch cookie cutter.) Repeat process with remaining 9 dough pieces, stacking and covering wrappers.

Step 4

Working with 1 dumpling wrapper at a time, spoon 2 teaspoons filling into center of wrapper, and spread slightly. Holding the wrapper flat in your hand, lightly wet edges of wrapper with water using your fingertip; fold in half to form a half-moon, pressing out the air as you seal the dumpling. Cradling the dumpling in one hand, use the thumb and index finger of your opposite hand to fold and pinch the sealed edge, forming pleats along the length of the dumpling. Transfer sealed dumpling to prepared baking sheet; cover with a slightly damp paper towel. Repeat process with remaining dough and filling to yield 40 dumplings.

Step 5

Prepare a wide pot or wok for a bamboo steamer, and add 1 inch of water. Bring to a boil over high, making sure water doesn’t touch bottom of steamer. Line bottoms of 2 stackable bamboo steamer baskets with cabbage leaves. Arrange 10 dumplings in a single layer in each steamer basket. Stack and cover steamer, and place in prepared pot. Reduce heat to medium-high, and steam dumplings until wrappers are glossy and slightly translucent, 5 to 10 minutes. Repeat steaming process with remaining 20 dumplings.

Step 6

Stir together soy sauce, vinegar, scallions, black pepper, and sesame seeds in a small bowl. Serve dumplings hot with sauce, garnished with Chinese chives and, if desired, chile oil.