Start by preparing the rice: Wash the rice vigorously with your hands for a few times until the water runs clear. Drain and soak the rice for at least 4 hours or up to overnight.
Drain the water and place the rice in a wide dish. Add a little water on the bottom to prevent the rice from sticking. Top off the rice with some pandan leaves.
Steam over medium-high heat for 30 minutes, or until the rice is done. Discard the pandan leaves and set aside the rice.
Pandan Juice
Blend together the pandan leaves and water. Strain the mixture and only keep the liquid. Set aside.
Pandan Sticky Rice
Combine the rest of the ingredients in a pan over medium heat until it comes to a boil. Add in the rice and use a spatula to fold the rice to let it absorb all the liquid. Remove and set aside.
Pandan Coconut Sauce
Combine the coconut milk, sugar, and salt in a pan/saucepan over medium-high heat, and bring it to a boil. Add in the cornstarch slurry and mix until there are no lumps and the sauce has thickened.
To Serve
Serve the rice with the sliced mangoes. Spoon some of the pandan coconut sauce on top and enjoy!