Make the raw glutinous rice dough: In a large bowl, add 300g glutinous rice flour. Gradually pour in 250g water while stirring with chopsticks until flocculent. Knead by hand into a smooth raw glutinous rice dough (no need to rest; use immediately).

Boil the dough: Fill a pot with enough water and bring to a rolling boil over high heat. Tear the raw dough into small pieces (about the size of walnuts) and add them to the boiling water one by one. Stir gently with a spoon to prevent sticking to the bottom of the pot or to each other.

Simmer until fully cooked: Once all the dough pieces float to the surface (this means they’re partially cooked), reduce the heat to medium-low and continue boiling for 7-8 minutes to ensure the insides are fully cooked (no raw centers).

Season and knead: Drain the cooked dough pieces well and transfer to a large bowl. While still hot, add 1 tbsp sugar and 1 tbsp cooking oil. Use a rolling pin to press and mash the dough until the sugar melts and the oil is well incorporated. Transfer the dough to a prepared mat and knead repeatedly until smooth and elastic (let it cool slightly for 2-3 minutes first to avoid burning your hands).

Roll out and dust with soybean flour: Dust the mat evenly with roasted soybean flour. Place the kneaded dough on top and dust the surface of the dough with more soybean flour (to prevent sticking during rolling). While the dough is still warm, roll it out into a neat rectangular sheet (about 0.5cm thick; roll with even pressure to avoid uneven thickness).

Fill and roll: Spread a uniform layer of 150g red bean paste over the rolled-out dough sheet (leave a 1cm gap around the edges to prevent the paste from oozing out when rolling). Tightly roll up the dough from one end into a thick, even log. Gently press the log with your hands to remove any air gaps inside.