Bring at least 6 cups (1.5 L) water to a full boil over high heat to cook the tapioca pearls. Make the coconut cream by placing the coconut milk and pandan leaf in a small pot and bringing the milk to a boil over medium heat. Add the sugar and salt; stir until dissolved.
Dissolve the rice flour in the water, then pour it into the coconut milk while you stir with a rubber spatula. Keep stirring constantly until the coconut milk returns to a boil and the mixture has thickened. Remove the coconut cream from the heat, discard the pandan leaf, and let cool.
Sprinkle the tapioca pearls into the boiling water and stir until the water returns to a boil. Then stop stirring and let them boil for 12 to 13 minutes. Meanwhile, prepare a small bowl of cold water to check doneness.
Check the doneness of the pearls by putting a small amount into the cold water. The pearls are done when any white centres remaining in the pearls look no larger than a tiny dot.
Drain the pearls through a metal fine-mesh sieve and run cold water through them until completely cool. Shake off excess water and transfer to a mixing bowl. If you’re not ready to serve, you can leave them at room temperature, covered, for up to 4 hours. For the best texture, it’s better to not refrigerate them.
To assemble, stir the coconut cream (it can be warm, room temperature, or cold) and the young coconut meat into the pearls, mixing well. You can taste the pudding with a piece of mango and add more sugar and/or salt as needed, depending on the sweetness and tartness of the mangoes.
Spoon into a small serving bowl and top with a generous helping of mango pieces. Serve within 30 minutes of mixing. The tapioca pearls will continue to absorb moisture from the cream as they sit, so the longer they sit, the less soft and creamy the texture will be. If you have any leftovers, you can store them in the fridge, but the texture will not be as good the next day.