Cut the sweet potato into cubes and steam for 10 minutes over high heat or until you can easily mash with a fork. Mash with butter and condensed milk while the potatoes are hot and use a rubber spatula to keep stirring until you get a smooth paste. Cover with a cling wrap to prevent the filling from drying. Chill in the fridge for at least 1 hour
220 gr purple sweet potato, 10 gr condensed milk, 10 gr butter
Lightly oil your palms and roll the mashed sweet potatoes into 24 round balls, about 10 grams each. Put this in the freezer to let it harden while you prepare the dough
Prepare the brown sugar ginger syrup:
Bring 4 cups of water to a boil. Add in ginger, screwpine leaves, and sugar. Bring it back to a boil and then lower the heat to let it simmer for about 30 minutes. Have a taste and add more sugar to your taste if necessary
4 cups water, 50 gr ginger slices, 100 gr brown sugar, 3 blades pandan leaves
Prepare the dough:
Put the tapioca flour in a large mixing bowl. Pour the hot boiling water (it has to be really hot) and stir with a spatula. When it's not too hot anymore, knead into a dough. If it's a bit too wet, add a bit of flour. If it's a bit too dry, you can add more hot water, teaspoon by teaspoon to get a smooth dough. Cover tightly with a cling wrap and let it rest for 5 minutes
140 gr tapioca flour/starch, 90 ml hot boiling water
Assembling:
Roll the dough into a long log and cut into 24 equal portions. Keep them covered and work with one dough at a time
Flatten the dough and roll into a disc, as thin as possible, about 1-2 mm . The thinner the dough, the more translucent the dough will be, but take care not to roll it too thin or it may break during boiling too
Put one filling on the center and then gather the edge to seal and pinch off any excess dough. Roll into a smooth round ball. Make sure the dough ball is smooth. Dab your palms with a bit of water and roll the dough ball if the dough turns dry. Repeat with the rest of the dough and filling
Cooking:
Bring a large pot of water to a boil. Put the tang yuan balls in and lower the heat to medium. Stir once or twice to make sure the tang yuan do not stick to the bottom of the pot. Let them cook until they float to the top, about 8 minutes. Turn off the heat and cover. Let them sit for 15 minutes. This is when the tang yuan will turn translucent
Remove with a slotted spoon into cold water to stop the cooking process. Keep them in the bowl of cold water until you are ready to serve. These also prevent them from sticking to each other
To serve:
Portion out the crystal tang yuan and ladle the brown sugar ginger soup over and tuck in