Soak the split mung beans in hot water for 30 minutes or 1 hour if using room temperature water. Discard soaking water. Place the soaked beans in a steaming dish along with pieces of pandan leaves. Steam the beans over high heat for 10-15 minutes or until the beans are soft with some bite to it and not mushy. Check at 10-minute mark to avoid over cooking. Remove from the steamer and discard the pandan leaves
Prepare the soup:
Place water,sugar, a tiny pinch of salt, and pandan leaves in a medium to large pot. Bring to a boil and cook until the sugar dissolves. Have a taste and adjust the sweetness level if needed. You can prepare ahead up to this point
When ready to serve tau suan:
Toast the you tiao briefly in toaster oven or air fryer until crispy and then cut into smaller pieces and set aside
Mix sweet potato starch with water. Bring the soup back to a boil. Add cooked beans and bring back to a simmer. Give the sweet potato starch solution a stir. While one hand is stirring, the other slowly pour in the sweet potato starch solution and keep stirring until the liquid is thickened. The beans should not sink to the bottom and suspended by the thick gooey soup. If the soup is not thick enough to your preference, you can thicken it with more starch and water mixture. Turn off the heat and serve with you tiao
Video
Notes
You can also use corn starch or tapioca starch, but the soup turns watery much faster compared to using sweet potato starch or potato starch