Peel the mangoes. Cut large slices from the front and back of the seed. Set aside.
In a microwave-safe bowl, combine mochiko, cornstarch, sugar, water, and milk. Mix until smooth.
Microwave the mixture for 2 minutes. Stir well, then microwave again for another 1–2 minutes until the dough turns translucent and sticky.
Let the dough cool slightly.
Dust your work surface generously with cornstarch.
Transfer the dough to the board and divide it into two equal portions.
Knead each portion lightly and roll.
Flatten one dough ball and place a mango slice in the center.
Pinch the edges of the dough together to seal, then flip it seam-side down.
Slice the mochi in half to reveal a beautiful mango cross-section before serving.
Enjoy!