Step 1

Add black sesame seeds and sugar in a food processor, grind until they achieve a sandy texture.

Step 2

Add in butter, water and salt. Do long pulses until the mixture becomes a paste.

Step 3

Transfer the black sesame mixture to a bowl, cover and store in the freezer while working on the dough.

Step 4

In a small sauce pan, bring two cups of water to a boil (for cooking the dough).

Step 5

In another bowl, mix the room temperature water with glutinous rice flour, stir until the water is absorbed by the flour.

Step 6

Squeeze and form a small piece of dough ball (around 1.5" diameter), press it flat and cook it in the boiling water until the dough floats.

Step 7

Add the cooked dough back into the flour mixture along with vegetable oil, and let it cool down a bit before kneading it into the mixture. Continue to knead until the dough is soft and smooth. Add more glutinous rice flour if it's too sticky, or more water if it's too dry. Cover with a damp towel to prevent it from drying out.

Step 8

Separate the filling into 20 portions and roll them into small balls. Cover and store in the freezer while working on the dough.

Step 9

Roll the glutinous rice dough into a log before cutting it into 20 little pieces. Roll all the small pieces into balls.

Step 10

To assemble the tang yuan, flatten a dough ball to form a approximately 2.5" (6 cm) round wrap with the edges thinner than the center.

Step 11

Place a piece of black sesame filling in the middle and wrap the dough around the filling. Finally, roll the tang yuan with your hand to form a ball. Repeat the previous step and this one for the rest of the tang yuan and coat them all with some glutinous rice flour.

Step 12

If you are not cooking all the tang yuans right away, it's best to freeze them right after you are done assembling.

Step 13

Heat a sauce pan over medium heat, add brown sugar in the pan, cook and stir until it starts to melt. This step is optional, but will help bring out the aroma of the sugar.

Step 14

Add water and ginger and bring it to a boil. The longer you cook this soup, the more ginger flavor you will get, so adjust this step to suit your taste.

Step 15

The soup won't taste very sweet if you use Taiwanese brown sugar. You can add more sugar if you want, but remember that the tang yuan is pretty sweet already.

Step 16

In a 2qt pot, bring 5 cups of water to a boil, place the Tang Yuan in the water carefully. Gently move them with a spatula or the back of a spoon to prevent from sticking to the bottom of the pot.

Step 17

Once the water boils again, decrease the heat to maintain a gentle boil and cook until the tang yuans float.

Step 18

Add ginger soup and tang yuan in a bowl and serve.

Step 19

Put the tan yuan in a zip lock bag. Line the bag on a tray and make some space between the tang yuan (so they won't stick together when freezing) and then store in the freezer. Once the tang yuan becomes harder, you can remove the tray as they won't stick together anymore now that they've hardened.