Place the chopped pandan and water into a blender and blend for 60-90 seconds until fully pureed. If you have a small blender pitcher, do this in two batches.
Strain the pandan liquid through a wire mesh strainer into a bowl, discarding the pulp. Press the pulp in the strainer to get as much of the liquid out as possible without pushing any of the pulp through the strainer.
Steam the taro cubes for 10-12 minutes or until fork tender.
Meanwhile, mix together the rice, blended pandan water, salt, sugar, vanilla, and tapioca starch in a pot.
Bring the mixture to a boil over medium-high heat, then lower the heat and let it simmer for 15 minutes with the lid on.
Gently fold the steamed taro pieces into the cooked rice. Be careful not to crush the taro while mixing.
In a saucepan, whisk together the coconut sauce ingredients.
Bring the mixture to a boil over medium heat, whisking occasionally, and cook for 4-5 minutes until smooth and thickened.
Portion the taro pudding into bowls, and top each serving with the coconut sauce. Optionally garnish with freshly grated coconut and palm sugar.