Pour water into a wok or stockpot and set a two-tiered bamboo steamer in the wok or on the rim of the stockpot. Make sure the water does not touch the bottom of the steamer. Line the steamer with a round of parchment. Cover and bring to a boil over high. Drain the mung beans and spread in parchment-lined steamer. Cover and steam until pale yellow and soft, about 20 minutes. Remove from the heat, transfer to a rimmed baking sheet and refrigerate until cool.
Put the sesame seeds in a food processor and pulse until ground. Add the cooled mung beans, fried shallots, 1/4 cup shallot or canola oil, salt and sugar and pulse until well blended. Set the filling aside.
To make the dough, in a small saucepan or a kettle, bring 2 cups water to a boil. Meanwhile, in a bowl, whisk together the tapioca starch, cornstarch, rice flour, sugar and salt. When the water is boiling, gradually add it to the flour mixture while stirring constantly. Then add the other 1/4 cup shallot or canola oil and knead it into the flour mixture with your hands until a smooth dough forms. The texture will be sticky and gooey, like taffy or melted mozzarella.
Dust a work surface with 1 tablespoon tapioca starch. Transfer the dough to the floured surface and knead for about 5 minutes, until it is smooth and soft, dusting the surface with additional tapioca starch as necessary to prevent the dough from sticking. It will have the texture and appearance of modeling clay. Divide the dough into 6 equal portions and cover them with plastic wrap.
Remove 1 portion of the dough from under the plastic wrap, leaving the others covered. Dust your work surface with tapioca starch and, using your palms, roll the dough back and forth on the work surface into a log 13 inches long and 1 inch in diameter. Cut the log crosswise into 13 even pieces. Cover the pieces with plastic wrap. Repeat with the remaining dough portions, making sure to cover all of the pieces as they are cut.
Lightly oil 2 rimmed baking sheets. To fill the dumplings, lightly flour your fingers with tapioca starch and, working with one piece of dough at a time (keeping the rest covered) roll the dough into a ball. Gently press the ball into a round about 2 inches wide.
Place 1/2 teaspoon of the filling in the center of the dough round, fold the round in half, and pinch the edges together to seal. Repeat with the remaining dough pieces and filling. As the dumplings are formed, place them on the prepared baking sheets and cover with plastic wrap.
Meanwhile, arrange as many dumplings as will fit in a single layer in each parchment-lined bamboo tier, spacing them so they don't touch. Return the water to a boil, then cover and steam. Cover and steam the dumplings for 6 to 8 minutes, until translucent and slightly shiny.
While the dumplings are steaming, make the dipping sauce. In a small bowl, stir together the soy sauce, 1/4 cup water, the vinegar, and sugar until the sugar has dissolved. Stir in the garlic and chiles.
When the dumplings are ready, remove the bamboo tiers from over the water and, using chopsticks or your fingers, carefully transfer them to a warmed large platter. Drizzle the dumplings with shallot or canola oil and serve the flavored soy sauce alongside. Repeat the steaming process with the remaining dumplings, replacing the parchment rounds for each new batch.
Makes about 48 2-inch meatballs
For the sauce
1 pound boneless pork shoulder, finely hand-chopped (see below), or coarsely ground pork shoulder
4 cups chicken stock or water
3/4 cup canola oil
1/4 cup minced garlic
1 Tbsp red pepper flakes
1 1/2 tsp ground annatto seeds
2 cups finely chopped shallots (about 5 large shallots)
2 cups finely diced yellow onions
1 cup stir-fry sauce
1 cup ketchup
1 1/2 Tbsp light soy sauce