Mix glutinous rice flour and icing sugar in a mixing bowl. Add the boiling hot water. Stir to mix with a spatula at first and when it's not too hot anymore, use a clean hand to mix and knead into a non-sticky dough. If you want to add some color, you can add it here. Add a bit of water as needed to form a dough. The dough will be soft and pliable because of the hot water. Cover them with plastic wrap to prevent them from drying out
Pinch off a small amount of dough, about 8-10 grams (it's up to you how big or small you want them to be) and then roll into small balls. You should have no problem with the dough breaking because the dough is so soft and pliable. Keep the small balls covered with plastic wrap too. Continue with the rest
Cook the tang yuan:
Bring 6 cups of water to a boil. When they are rolling boil, add the tang yuan balls and cook until they float to the top. Once they float to the top, keep stirring the soup while the other hand gradually pours in the beaten egg. Once the egg is set, turn off the heat. Stir in goji berries. The residual heat will soften the goji berries. Add the sweet rice wine to the soup. Portion the tang yuan with the soup and rice wine into serving bowl.