Instructions

for the soup

Place 8-inch square baking pan in freezer. Sprinkle 1 tablespoon unflavored gelatin over 1 cup water in small saucepan and let sit 2 minutes to hydrate. Add 1 coarsely chopped scallion, 1 tablespoon chopped ginger, and ¼ teaspoon chicken base. Bring to boil; lower heat to gentle simmer and cook for 8 minutes. Strain through fine-mesh strainer into 2-cup liquid measuring cup. If liquid is more than ½ cup, return to saucepan and boil until reduced to ½ cup.
 2. Add ¼ cup ice cubes until liquid measures ⅔ cup (you will not need all of ice). Stir until ice is melted. Pour into prepared pan and refrigerate until firm and bouncy, about 20 minutes. While soup sets, make dough.

for the dough

Whisk 2 cups (10 ounces/284 grams) all-purpose flour, 1 teaspoon sugar, ¾ teaspoon instant yeast, and ¼ teaspoon table salt together in bowl of stand mixer. Add 1 tablespoon vegetable oil and ¾ cup (6 ounces/170 grams) room temperature water. Fit mixer with dough hook and mix on low speed, scraping down bowl if needed, until no dry flour remains, about 2 minutes. Increase speed to medium-low and knead until dough is smooth and elastic, about 10 minutes. Shape dough into ball and transfer to lightly greased bowl. Cover and let rise until slightly puffy, about 20 minutes. Remove any excess dough from mixer bowl but do not wash.

for the filling

Whisk 1 tablespoon water and ¼ teaspoon baking soda together in now-empty mixer bowl. Add 8 ounces ground pork and toss to combine. Add 2 tablespoons minced scallions, 1 tablespoon grated ginger, 2 teaspoons Shaoxing wine, 2 teaspoons soy sauce, 1½ teaspoons minced garlic, 1½ teaspoons toasted sesame oil, 1 teaspoon sugar, ½ teaspoon salt, and ⅛ teaspoon white pepper. Fit mixer with paddle and beat on medium speed until mixture is well combined and pork has slightly lightened in color and become stringy, about 90 seconds.
Spray large plate with vegetable oil spray. Using fork, mash soup into ⅛-inch pieces. Add to pork and mix on medium-low speed until incorporated, about 30 seconds. Divide filling into 16 portions (about 1 heaping tablespoon each) and arrange on prepared plate. Refrigerate until needed.
Press on dough to deflate. Transfer to counter and roll into 16-inch cylinder. Cut into 16 equal pieces (1 ounce/28 grams each). Roll each portion into ball. Place balls on lightly floured counter, dust with flour, and press each into 2-inch disk. Cover with damp dish towel.
Roll one disk into 3-inch round. Holding wrapper with your hand, continue rolling outer 1 inch of dough, rotating dough slightly after each roll to maintain uniform shape, until you have 4½-inch round with tapered edges. Re-cover wrapper and repeat with remaining disks. Do not overlap disks. Brush 12-inch nonstick skillet with 2 tablespoons vegetable oil. Place 1 wrapper on lightly floured counter and place 1 portion filling in center. 
Pinch outer edge of dough together with your thumb and index finger and hold. Using other thumb and index finger, push edge of dough toward pinched portion to create first ¼-inch pleat. Pinch pleat to seal and continue pinching to secure dough while creating next pleat. Push dough toward pinched portion to begin forming second pleat. Repeat pleating motion, rotating dough with each pleat, until all of dough is pleated and dumpling has rounded shape. Pinch top of gathered dough edges together and twist to seal dumpling. Place dumpling pleated side down on counter. Press gently to secure seal and round sides. Transfer to prepared skillet, pleats side down. Repeat with remaining wrappers and filling. Cover skillet with plastic wrap and let rise for 30 minutes.
Discard plastic wrap and place skillet over medium heat. Cook until bottoms of dumplings are golden brown, about 4 minutes. Reduce heat to medium-low; carefully pour ⅓ cup water around edge of skillet (water and oil will spatter). Cover and continue to cook until water is absorbed, about 8 minutes. Uncover and continue to cook until dumpling bottoms are deep golden brown and crispy, about 4 minutes longer. Sprinkle with 1 thinly sliced scallion and 1 teaspoon black sesame seeds. Serve immediately, passing Chinese black vinegar separately, if using.