Strain the batter
Glutinous rice flour can leave small lumps even after thorough whisking. Passing the batter through a fine-mesh strainer gives the finished layers a smoother texture.
Divide the batter evenly
Weighing the three portions is the easiest way to create layers of similar thickness. If you are dividing by eye, use identical bowls and compare their levels before adding the colors.
Stir before pouring
Rice flour can settle while the other layers are steaming. Stir each bowl gently before pouring it into the pan so the flour is evenly distributed again.
Let every layer set
The surface should appear firm and should not leave wet batter on a lightly touched spoon or spatula. If the previous layer is still liquid, the next color can sink into it and blur the separation.
The first two layers only need to become firm enough to support the next one. Give the final layer enough time for the entire cake to cook through.
Pour gently
Hold the bowl close to the surface and pour slowly. You can also pour the batter over the back of a spoon to soften its impact on the layer underneath.
Control condensation
Wrap the steamer lid with a clean kitchen towel so condensed water does not drip onto the batter. Keep the loose ends of the towel safely away from the flame.
Watch the steamer water
Sapin-sapin requires a fairly long steaming time. Check the water between layers and add more hot water when needed so the steamer does not run dry.
Cool before unmolding
Warm sapin-sapin is still very soft and can stretch or tear. Let it cool completely before loosening the edges and turning it onto a serving plate.
Watch the latik closely
Coconut curds darken quickly near the end. Lower the heat and stir more frequently once the oil begins to separate. Remove the curds when they are golden brown because they continue cooking briefly in the hot oil.