Drain the soaked sticky rice and steam in a bamboo steamer or steamer basket lined with cheesecloth for 25-30 minutes, until grains are tender with no hard center when pressed.

While rice is still hot, transfer to a bowl and mix in 1/2 cup coconut milk, 3 tablespoons sugar, and salt. Stir gently until the liquid is absorbed and rice is glossy. Let cool for 10 minutes, then fold in diced mango. Set aside.

For the mochi wrapper, whisk together sweet rice flour, 1/4 cup sugar, water, remaining 1/4 cup coconut milk, and coconut cream in a microwave-safe bowl until completely smooth with no lumps.

Cover bowl with plastic wrap, leaving one corner vented. Microwave on high for 2 minutes, stir well, then microwave in 1-minute intervals, stirring between each, until the mixture becomes translucent, stretchy, and pulls away from the sides (about 4-5 minutes total).

Dust a clean work surface generously with cornstarch. Turn out the hot mochi dough and dust the top with more cornstarch. Let cool for 2-3 minutes until just cool enough to handle.

Divide the mochi dough into 8 equal pieces. Dust your hands with cornstarch, then flatten one piece into a 4-inch circle. Place 2 tablespoons of the mango rice filling in the center.

Gather the edges of the mochi up and around the filling, pinching firmly to seal. Roll gently between your palms to smooth the seam, then place seam-side down. Repeat with remaining dough and filling.

Dust off excess cornstarch with a soft brush. Serve immediately at room temperature, or store in an airtight container.