In a microwave-safe bowl, combine the ¾ cup glutinous rice flour, ¼ cup sugar, and ¾ cup water. Whisk together until combined.
Microwave the bowl on high for 1 minute. Remove, and use a spatula to mix together. Lumps are expected. Return to the microwave and heat another 30 seconds. Remove and stir. Return to the microwave for 15-30 second increments until all liquid becomes a sticky dough.
Ensure the dough is cool enough to handle before proceeding. Sprinkle your board generously with cornstarch, and roll out to about ¼" thickness. Cut out 2" circles.
Remove the ice cream balls from the freezer and add one ½ tsp filling to the center of your mochi dough circle. Fold it up and press together the seams. Set aside (recommend putting right back into the freezer) and repeat for all remaining filling and dough.
You can eat them immediately, but the ice cream may be melty or soft given handling outside the freezer. I recommend allowing them to set in the freezer for at least 1+ hours before serving.