Line a baking sheet with parchment paper. Using a 2-ounce ice cream scoop, form 8 tight ice cream balls and place them on the prepared sheet. Freeze for at least 2 hours until rock-solid.

In a microwave-safe bowl, whisk together the sweet rice flour, sugar, and water until completely smooth with no lumps remaining.

Microwave the mixture uncovered on high for 90 seconds, then stir vigorously. Microwave for another 60 seconds, stir again — the dough should look translucent and stretchy. If still cloudy in spots, microwave for one final 30-second burst.

Dust a clean work surface generously with cornstarch. Turn the hot mochi dough out onto the surface and dust the top heavily with more cornstarch. Let cool for 10 minutes until warm but safe to handle.

Pat the dough into a rough rectangle about 1/4-inch thick. Using a 4-inch round cutter or bowl, cut out 8 circles, re-rolling scraps as needed and adding more cornstarch if sticky.

Working with one ice cream ball at a time (keep others frozen), place it in the center of a mochi circle. Quickly gather the edges up and around the ice cream, pinching firmly to seal at the top. Twist off any excess dough.

Place the wrapped mochi seam-side down on the parchment-lined sheet. Repeat with remaining circles and ice cream balls, working as quickly as possible.

Freeze the finished mochi for at least 1 hour before serving. The mochi shell will soften slightly in the freezer to the perfect chewy texture.