Set up your steaming station. Stack a 3-tiered bamboo basket into a wok and fill with water. Heat the water on medium heat and wait until there are thick, steady clouds of steam.
Note: the water should not be a roiling boil but it's not a gentle bubble either. There should be enough bubbles coming from the bottom of the wok/pot to provide steady, consistent steam. But not so much that it bubbles furiously and touches the bottom cake pan.
Grease 3 tinfoil cake pans well with vegetable oil. (Any neutral oil works.) When the water is steaming, add 3/4 cup of Coconut Milk Batter to each pan. I transfer batter into a measuring cup, making sure it measures 3/4 cup exactly. Then I use a small spatula to scrape into the tinfoil cake pan. The batter is quite thick so scraping is a necessary step for measurement accuracy. Repeat for all cakes.
Steam until the first layer sets, about 7-9 minutes. Gently shake the pan -- there should be no jiggle. It's ok if it looks bumpy. If the first layer is too soft, the red bean filling will sink through the batter and be difficult to spread.
Remove from heat and layer red bean filling on top. Make sure the red bean filling is evenly leveled and leave a 1/2-inch edge for sealing. Repeat for all cakes.
Add additional 3/4 cup of Coconut Milk Batter directly on top. It should cover the red bean filling and go all the way to the edge. Repeat for all cakes. Steam until cooked through, an additional 45 minutes. Check the water, from time to time, to make sure the water does not run out. When a skewer comes out clean, it's done.
Cool completely and invert onto a platter. Serve and enjoy! This cake tastes best the day it's made. Leftovers should be wrapped tightly with plastic wrap and placed in a air-tight container.