Coat 8-inch/20-cm square baking pan with oil, then line with non-stick baking paper.
*For grated cassava: You will need 1.7-1.8 kg of cassava. Make a shallow cut on the skin of cassava, peel off the skin with knife, rinse with water. Remove the tough fibre in the centre. Finely grate cassava with food processor. Measure out 1.3 kg of grated cassava (no need to drain off the liquid).
Add salt and tapioca starch to grated cassava, mix well. Add in thick coconut milk gradually, mix until combined.
Divide into 3 equal portions, each about 570 g.
For plain layer: Add fine sugar and water to 1 portion of cassava mixture, mix well. Pour into lined baking pan, steam over medium heat for 8 minutes.
*Pandan juice: Blend 15 g of pandan leaves with 45 g of water, extract 35 g of pandan juice.
For pandan layer: Add fine sugar and pandan juice to 1 portion of cassava mixture, mix well. Pour pandan layer over plain layer, steam over medium heat for 8 minutes.
Sift dark brown sugar to remove coarse part, take out 75 g of fine dark brown sugar.
For brown sugar layer: Add dark brown sugar and water to cassava mixture, mix well. Pour brown sugar layer over pandan layer, smooth the surface with spatula, steam over medium heat for 1 hour.
Set aside to cool completely.
Unmould when completely cooled, cut into pieces using plastic knife.