Peel, cut and steam the purple and orange sweet potatoes (with pandan leaves) for about 20 minutes.
To prevent the purple sweet potatoes from staining the orange sweet potatoes, steam the 2 types of sweet potatoes in separate trays.
ORANGE SWEET POTATOES
Add ginger slices and crushed pandan leaves and boil for about 10 minutes
Add rock sugar and stir until it dissolves completely
Add steamed orange sweet potatoes and dried longans and bring it to a boil. Turn off the flame and cover the pot.
PURPLE SWEET POTATOES
In the same way, boil purple sweet potatoes in water with ginger slices and pandan leaves; add rock sugar and purple sweet potatoes. Turn off the flame and cover the pot.
SERVING
Serve orange and purple sweet potatoes, longans with ginger water for a refreshing hot or chilled dessert.