In a medium saucepan over low heat, stir together the butter, black sesame powder, sugar, and Shaoxing wine until smooth.
200 g unsalted butter, at room temperature, 200 g black sesame powder, 225 g granulated sugar, 1 teaspoon Shaoxing wine
Remove from the heat and let cool completely (freeze for 15 to 20 minutes if needed).
Roll the mixture into 1-teaspoon balls with your hands. Set aside.
Place the glutinous rice flour in a large bowl. Add the water a little at a time, kneading until the dough resembles modeling clay—smooth and pliable, not too soft.
500 g glutinous rice flour, 118 ml water
Bring a large pot of water to a boil over high heat. Meanwhile, form the dumplings.
Pinch off a piece of dough about the size of a golf ball. Roll into a ball, then use your thumb to press a deep indentation in the center.
Place a sesame ball in the indentation and seal it completely inside the dough. Make sure the dough is tightly sealed around the filling. Smooth the seams with slightly moistened fingers, dusting with a little flour if needed. Repeat with the remaining dough and filling.
Cook the dumplings in the boiling water over medium-high heat, gently stirring in one direction so they don't stick. When they float to the surface, reduce the heat to medium-low and cook for 1 minute more.
Lift the dumplings out with a slotted spoon as they finish cooking. Blot gently on a clean towel, transfer to a large dish, and serve.
Alternatively, serve in a warm bowl with a light syrup of water, sugar, and orange blossom water.
Notes
Glutinous rice flour and black sesame powder are available in most Asian supermarkets. If you can't find black sesame powder, grind black sesame seeds in a food processor until finely powdered.
The amount of water needed for glutinous rice flour can vary widely depending on your local humidity and even the age of the flour.
Glutinous rice flour can be a little tricky. At first the dough may look too dry, and 20 seconds later it may stick to your hands because you've added too much water. If that happens, work in a little more glutinous rice flour. If the dough is too dry, add more water—just a tiny amount at a time.