Xiao long bao, or soup dumplings, are Chinese steamed dumplings that have soup inside of them. They are like magic! I grew up eating these with my family at our favorite dim sum restaurant in Chicago's Chinatown and later learned how to make them by combining my family's go-to pot sticker recipe with the secret ingredient: soup gelatin, which melts down into soup once the dumplings are cooked.
For the wrappers: Combine the flour and salt in a large bowl and create a well in the middle. Add the boiling water and mix it in with a spatula, then incorporate with your hands until you have a mealy, shaggy mixture. Mix in the cold water and bring everything together into a dough, then turn it out onto a work surface and knead, adding additional flour if it gets too sticky to work with, until you have a smooth and slightly sticky dough, 7 to 10 minutes. Cover with plastic wrap or a damp towel for 30 minutes while you make the filling.
For the soup: Heat the chicken stock, then add the soy sauce and gelatin powder. Whisk to combine. Pour into a shallow dish and chill until set, around 1 hour. Break up the gelatin by fluffing with a fork. Set aside.
For the filling: Put the pork in a large bowl and sprinkle on the salt, then add the soy sauce, ginger, sambal oelek, sesame oil, rice vinegar and scallions. Mix everything together with your hands (don't overmix), then set up your dumpling folding station.
Line a sheet pan with parchment paper and dust with flour. To assemble the dumplings, divide the dough into 32 balls and keep them covered when you're not working with them. Roll them out into 3 1/2- to 4-inch circles, flouring the surface as needed. Place 1/2 tablespoon pork filling in the center of each circle and 1/2 tablespoon soup gelatin on top of the filling. Fold up the edges of the dumpling and pinch everything in the center. Repeat with the remaining dumpling wrappers and filling and place on the lined sheet pan.
To steam the dumplings, line a bamboo steamer with cabbage leaves or parchment paper with a few holes cut out. Place the dumplings in the steamer, leaving a little bit of room between them, then set the steamer over a pot of boiling water. Steam in batches until cooked through, 8 to 10 minutes. Alternately, line a plate with cabbage leaves or parchment paper. Place in a pot of boiling water, making sure the water doesn't cover the plate (you will need about 1/2 to 3/4 cup). Cook 8 to 10 minutes.
Let cool slightly, then enjoy with a sauce of equal parts vinegar and soy sauce with sambal oelek to taste.
Assembled soup dumplings can be frozen, then steamed directly from the freezer for 8 to 10 minutes.