Add the rice to a medium size mixing bowl and cover with cold water to fully submerge. Cover with plastic wrap and let sit in the fridge overnight, or 3-4 hours minimum.
Fill a large sauce pot with 1-2” (2.5-5cm) of water and bring to a simmer of medium-low heat. Place a steamer basket over the water and line with a layer of cheesecloth, making sure to leave about 1-2” (2.5-5cm) of overhang around the perimeter of the basket.
Drain the soaked rice in a fine mesh colander then transfer in 1 even layer to the steamer basket. Cover and steam the rice just until chewy, mochi-like, and no dry crunchy bits remain, about 20-30 minutes.
In a small saucepot, combine half of the coconut milk, half of the sugar, all of the salt, and the cardamom pods. Bring to a simmer over medium high heat, stirring occasionally, and cook until the sugar is dissolved. Remove from the heat, cover, and keep warm until the rice is done.
In another small saucepot, combine the remaining coconut milk and sugar. Cook, stirring occasionally, over medium heat until simmering and the sugar is dissolved.
In a small sized mixing bowl, whisk together the corn starch and a couple tablespoons of the coconut mixture. Stir the slurry back into the coconut mixture and continue to cook while constantly stirring just until thickened and glossy. Allow to cool and place in a serving cup for drizzling. Adjust consistency with water if desired as this mixture will thicken more when it cools.
Once the rice is done, remove the cardamom pods from the first coconut mixture. Transfer the rice to a large sized mixing bowl and cover with the coconut mixture. Gently stir to thoroughly combine. Cover and let sit at room temperature to properly absorb the liquid for at least 30 minutes and up to 3 hours before serving.
Pack ½ cup of the rice into a small bowl then invert onto a large plate. Fan the sliced mango alongside the rice then top the rice with the thickened coconut sauce and toasted sesame seeds. Serve and enjoy!
