Wash and rinse 1/2 cup black sesame seeds a few times to remove dust and impurities. Then, pan fry them on a pan with low heat until it’s dried.
After that, put the black sesame seeds into a chopper. Chop until it’s fine and small. Then, add 1/2 cup of sugar and chop with the black sesame seeds. Next, add 1 stick (8 tablespoons) of unsalted butter and chop until it mixed well.
After, put the black sesame paste filling in a freezer for 5-10 minutes, so they are little bit harder and easy for rolling. Then, roll them into little balls. And, freeze the black sesame balls overnight. (You can roll them into balls and save it. Don’t need to use them all at once.)
In a container, add 1 cup of glutinous rice flour and 1/2 cup of warm water. Mix them and knead them into a dough. (If it is too dry, add 2 teaspoons of water little by little. You can double the flour dough recipe if you want to use all the black sesame balls all at once.)
Roughly divided the dough into small pieces.
Flatten the dough into a circle shape. Try to make the side thinner, but middle thicker. Put the frozen black sesame ball in the middle of the dough. Then, close up and roll into a ball. (If the dough is too dry, dip some water on your hand and roll the dough.)
Boil water in a pot, wait until water is boiling. Add tang yuan into water and let it boil until they float on the top. When they are floating on top, it is a good sign to know they are done.
At the meanwhile, in another pot pour 2 cups of water, 1/2 cup of brown sugar and 4 slices of ginger. Let it boil for 5- 10 minutes.
When the tang yuan is ready, pour the sugar water over and serve.