Make the Yellow Mung Bean Batter

1. Wash dried mung beans until water runs clear then transfer to a small pot. Add water to cover by 1½ inches. Cook until softened on medium-low heat, uncovered (about 20 minutes).
2. To a blender, add cooked mung beans, salt, tapioca starch, rice flour, coconut milk, vanilla extract, and sugar. Blend until smooth. Pass the mixture through a sieve to remove clumps. The mixture will have the consistency of pancake batter.

Make the Green Pandan Batter

1. Rinse the blender. Cut pandan leaves into small pieces. Add cut leaves and water. Blend until smooth. Strain liquid through a sieve to extract the liquid and set it aside. Discard the pandan pulp.
2. In a large mixing bowl, mix together pandan water, tapioca starch, rice flour, glutinous rice flour, sugar, salt, coconut milk, and pandan gel extract. Pass the mixture through a sieve to remove clumps. The mixture will be much thinner in consistency than the yellow batter.

Divide the Batter and Steam the Layers

1. Use a large steamer that will fit a 9-inch circular cake pan with a depth of at least 2 inches. You can also use two smaller cake pans. Get the steamer ready by filling the basin halfway with water. Bring the water to a medium simmer. Have some kitchen towels handy to wipe down the inside of the steamer lid. This will prevent water from falling onto the cake while steaming.
2. Divide the green batter equally between 3 bowls. Divide the yellow batter equally between 2 bowls. The cake will have 5 layers, starting and ending with the green pandan layer.
3. Brush vegetable oil on the bottom and the sides of the pan. Steam the oiled pan by itself for 5 minutes. Add the first bowl of green batter. Warning: It will be hot but you will have to pour slowly, close to the pan, to prevent bubbles. If there are bubbles, you can scoop them away with a spoon (purely for aesthetics) or leave them be. Steam for 5 minutes.
4. Open up the lid and give it a quick wipe down on the inside. Add a bowl of yellow mung bean layer. Steam for 7 minutes. Continue this pattern until all batter is gone. 5 minutes for green. 7 minutes for yellow. Make sure to wipe down the inside of the lid each time a new layer is added.
5. Carefully remove the cake from the steamer and allow the cake to cool completely before cutting.