Mix the glutinous rice flour and all-purpose flour together. Add the gac seeds and knead until the red pulp is mixed in, then discard the seeds. Gradually add water and knead until the dough is slightly sticky and elastic. Let the dough rest for about 30 minutes.

After 30 minutes, knead the dough again. If it's dry, add a little more water. Knead until you can pinch off a piece and it slowly stretches and droops—then it's ready.

For the filling: Add the mung beans to a pot with water (water should cover the beans by twice their height). Add salt and cook until the beans are soft and fully cooked. Puree the beans in a blender, then strain for a smooth texture. Transfer the strained beans to a nonstick pan, add vegetable oil and sugar, and cook over medium heat, stirring until the filling thickens and becomes slightly sticky. Let cool, then roll into small balls.

Divide the dough into even pieces and flatten each one. Place a ball of filling in the center, then gently wrap the dough around the filling, rolling between your hands to seal. Pinch off any excess dough and place the dumpling on a tray. This helps keep the filling centered when cooking.

Bring a pot of water to a boil. Roll the dumplings into smooth balls and drop them into the boiling water. When they float to the surface, transfer them to a bowl of cold water.

To make the syrup, caramelize sugar with a little water until lightly golden, then add more water and thinly sliced ginger. Bring to a boil, then add the dumplings. Simmer for another 5-7 minutes.