Wash the pandan leaves and cut them into small pieces. Blend the leaves with the water in a blender until smooth. Strain the mixture through a clean cloth or fine mesh sieve to extract the pandan juice.
In a bowl, combine the tapioca starch, rice flour, glutinous rice flour, sugar, coconut milk, salt, pandan juice, and vanilla extract. Mix well, then strain the batter through a sieve to ensure it is smooth.

Soak the mung beans for 2 to 4 hours. Rinse well, then steam the beans until cooked through.
Once cooked, let the beans cool slightly. Add the mung beans and sugar to a blender and blend until smooth. Add the tapioca starch, rice flour, coconut milk, and vanilla extract, and blend again until smooth. Strain the mixture through a sieve for a fine batter.

Prepare a steamer with plenty of water. Lightly grease the inside of your cake pan with oil and place it in the steamer. Pour a layer of the pandan batter into the pan.
Steam for about 5 minutes until set, then pour a layer of the mung bean batter over the cooked layer. Continue steaming until the layer is set.

Next, pour a third layer of pandan batter and steam until set. Repeat the process, alternating layers, until all the batter is used or the pan is full.

Once the final layer is cooked, remove the pan from the steamer and let the cake cool completely. Run a sharp knife around the edge to loosen, then invert the pan onto a plate to release the cake. Slice and enjoy with your family!