Grease a 20 cm / 8-inch square heatproof pan and set it aside. Fill a steamer pot with water and bring it to a rolling boil. Wrap the steamer lid in a clean kitchen towel to catch condensation.

Whisk the rice flour, tapioca flour, sugar, and salt in a mixing bowl. Whisk in the water and pandan paste until smooth, then pour through a fine-mesh sieve to catch any lumps.

Give the batter a final whisk, since the flour settles fast, and pour it into the prepared pan. Steam covered for 15 to 18 minutes until the surface looks matte and set and doesn't wobble when you nudge the pan.

While the bottom layer steams, whisk the coconut milk, rice flour, tapioca flour, and salt in a separate bowl until smooth. Strain through the sieve to remove lumps.

Once the bottom layer is set, whisk the coconut batter again and pour it gently over the top, spreading it evenly with the back of a spoon.

Steam covered for 20 to 25 minutes until the top layer is firm to the touch and no longer liquid in the center.

Turn off the heat, uncover the pan, and let the cake cool at room temperature for 30 minutes.

Refrigerate for 1 hour, then cut into 9 squares with an oiled knife, wiping the blade clean between cuts.