Scrape the sesame paste into a bowl. Heat 1 tablespoon oil in a small skillet until hot; then pour it over the sesame paste and stir it in until the sesame paste is soft and pasty. Add the red bean paste and cassia blossoms and stir in circular motions until well blended. Put the bowl in the refrigerator and chill for 30 minutes until the filling is firm. Divide it into 16 portions and roll them in the palm of your hand to make small balls. The filling can be made long in advance. Cover and refrigerate.
Making the dumplings
Add the ½ cup cold water to the glutinous rice powder, mixing and squeezing with your hands until a dough forms; add more cold water little by little until the dough holds smoothly, not flaking when you pinch or flatten it. Roll it out into a long sausage about 16 inches long; then cut the sausage into 16 pieces.
Press each piece of dough into a small disk, place a ball of filling in the center, fold over the side, pinch the seam closed, and then roll with your palms to make a small ball. Repeat until all 16 dumplings are formed. The dumplings may be made in advance. Cover and refrigerate.
Boiling the dumplings
Bring 6 cups of water to a rolling boil in a large saucepan; drop in the balls one by one, and let them toss in the vigorously boiling water over medium-high heat for about 5 minutes, until they float and spin to the top of the water. Scoop them into individual bowls and cover with some of the water. Serve immediately, 4 to a bowl.