Sift together 1 cup mochiko, 2 tablespoons matcha powder, and 3/4 cup granulated sugar in a microwave-safe bowl to remove lumps and distribute matcha evenly.

Pour 3/4 cup water into the dry mixture and stir vigorously with a rubber spatula until you have a smooth, lump-free batter.

Microwave the mixture uncovered on high for 2 minutes, stirring halfway through after 1 minute, until the dough turns translucent and becomes very thick and sticky.

Let the cooked mochi dough rest for 3 minutes to cool slightly and set, making it easier to handle.

While the mochi rests, spread 2 tablespoons of cornstarch on parchment paper and in a shallow dish for dusting to prevent sticking.

Use a damp spatula to transfer the mochi dough onto the cornstarch-dusted parchment paper and dust the top generously with cornstarch.

Allow the mochi to cool for 15 minutes until firm enough to cut but still flexible, then cut into 12 equal pieces with a lightly oiled knife or cookie scoop, wiping the blade between cuts.

Quickly roll each piece between your palms to form smooth balls, rolling in cornstarch to coat all sides, and transfer to a clean surface or storage container.

Once cooled completely, dust the mochi balls with 1/4 cup powdered sugar for a sweet finish and to prevent sticking.