Make the pandan extract: coarsely chop the Pandan Leaves, blend them with about 1/4 cup of Water until fragrant, then strain through a fine sieve or cheesecloth to collect fresh Pandan Juice. Set the juice aside.
In a large bowl whisk together the dry ingredients: Tapioca Starch, Rice Flour, Arrowroot Starch, Granulated Sugar and a pinch of Fine Salt until evenly combined.
Warm the Coconut Milk gently (do not boil) and gradually whisk it into the dry mixture, adding additional Water as needed to make a smooth, pourable batter with the consistency of heavy cream; strain if necessary to remove lumps.
Divide the batter into two portions — keep one plain and color the other by stirring in enough of the prepared Pandan Juice to achieve a rich green hue and fragrant flavor.
Lightly grease a shallow heatproof pan or baking dish with Neutral Oil and set up a steamer with simmering water. Cover the steamer so it holds steady steam.
To build the layers, pour a thin even layer (about 2–3 tablespoons for a small pan) of the plain batter into the pan and steam, covered, for 3–4 minutes until the layer is set but still tender. Repeat with a layer of the pandan batter, steaming each layer 3–4 minutes. Continue alternating plain and pandan layers until all batter is used, finishing with a steamed top layer.
After the final layer has been steamed, steam the entire cake for an additional 10–12 minutes to ensure the whole dessert is fully set.
Turn off the heat and leave the steamer slightly ajar to cool slightly, then remove the pan and allow the khanom chan to cool completely to room temperature (chilling makes slicing cleaner).
Run a knife around the edges, invert or slice the layered cake into small squares or diamonds and serve. Store leftovers covered in the refrigerator for up to 3 days.
