Wash the pandan leaves. Fold them and tie them into a knot.
Scrub and peel off the skin of the sweet potatoes and the yam.
Cut the sweet potatoes and yam into 2 cm cubes.
Place the sweet potatoes and the yam on a steaming plate, and start to steam straightaway. (See step 1 of Cooking Method)
Sieve 100 gm of tapioca flour in a bowl. Slowly add 75 ml of hot boiling water to it, using a pair of chopstick to stir it until it becomes lumpy.
Once it is cooled, use your hand to knead the mixture until it is smooth and forms a dough.
Divide the dough into 3 portions. Dab 3 drops of red, blue and green coloring with a chopstick to the 3 portions of dough respectively. Make sure you wipe the chopstick before dipping it into the next color.
Knead the three sets of colored dough until the color is well incorporated to form a uniformly coloured dough.
Put some tapioca flour on a board and a knife. Roll the dough into a long strip with your palm, and cut it into 1 cm lengths. Sprinkle some tapioca flour over the cut pieces to prevent them from sticking to one another. Repeat the process until all the dough is done.
In a wok, add water to the same level as the steaming stand and bring it to a boil. Place the tray of sweet potatoes and yam to steam immediately. Steam for about 20 mins until they are soft.
After preparing the tapioca dough cubes, put the cubes into a separate pot of boiling water. Continue to boil for about 5 mins until the tapioca cubes float up or turn translucent.
Transfer the tapioca cubes into a bowl of water to soak, and set aside for later use.
Meanwhile, add 700 ml of water, 130 gm of sugar and pandan leaves into a big pot and bring to a boil for about 15 mins until the sugar dissolves.
Lower the heat and add in the coconut milk and salt, then let it simmer for 10 minutes. Do not let it boil till it bubbles vigorously and do not cover the pot. Then turn off the heat. Remove and discard the pandan leaves.
Put the sweet potatoes, yam and cooked tapioca jelly into individual bowls. Add coconut soup and serve.
For a better and creamier flavour, it is best to use fresh coconut milk for the coconut soup. Here how to make coconut milk from scratch.