Heat pandan juice until it reaches 100 °F (38 °C), then pour it into the bowl of your stand mixer. Sprinkle sugar and yeast over top. Wait 5–10 minutes for the yeast to bloom (you can skip the wait if using instant yeast).
Once the yeast is foamy, add flour, oil, and salt.
Using the dough hook attachment, mix on medium speed until the dough starts to come together into a ball. Switch to the kneading setting (typically the second-lowest speed on most mixers) and knead for 12 minutes.
Place the dough in a lightly-oiled bowl and let rise in a warm place for 1 ½ hours.
Divide the dough into 16 pieces (65g each). It’s easiest to first divide it in half, then divide each piece in half again, and so on.
Flatten each piece of dough into a rough 6-inch circle. Place 3 tbsp (45g) of red bean paste in the center of each dough. Gather together the sides of the dough and pinch them together so the bean paste is completely wrapped in dough.
Arrange the buns on a baking sheet. Cover and let rise for another 20 minutes. While the dough is rising, preheat oven to 350 °F (175 °C).
Optional: Set another baking tray on top of the buns as they bake, to give them a flat, even shape.
Bake for 25 to 30 minutes, or until the tops are light golden brown.