In a pot of hot water, add the cinnamon stick and then the red beans. Let it cook for an hour in simmering water.
Drain, check that the beans are completely cooked, then remove the cinnamon stick.
Add the brown sugar and a little salt.
Mash with a spatula until you get a paste (I recommend using a blender for a better result).
Then put the rice flour in a bowl, add the white sugar and mix.
Gradually add lukewarm water to bind the flour. Knead as you go until you get a firm consistency.
Form balls of about 10 to 13 g with your hands. Make a hollow, add a little bean paste in the center, then reshape the ball.
Cook the Gyeongdan in boiling water (about 4-5 min) until they rise to the surface.
Coat them in your choice of soybean, mugwort, and sesame seed powders.
Notes
Feel free to add more sugar to the powders if it's not sweet enough for you. And if you can't find the powders I used, you can also coat them in coconut powder, cocoa powder, crumbled cake, roasted sesame seeds, etc...