Use an electric whisk to knead all of the ingredients for the dumpling dough. Leave the dough covered for one hour in a warm place.
Next, split the dough into six equally-sized pieces. Flatten each piece of dough into small round disks. Place a large teaspoon of plum jelly into the center of each dough disk. Enclose the plum jelly and form a ball using your hands. Make sure that the filling stays inside. Leave the dumplings for another 15 minutes in a covered bowl.
Cook the dumplings in a sieve over a water bath for 12 to 16 minutes. When serving, pour some vanilla sauce on the dumplings before sprinkling some poppy seeds and powdered sugar on top.