Scoop out the ice cream in smaller portions (you can use an ice cream scoop for this) and freeze it (this will help you work with the ice cream easily when forming the mochi - instead of working with the whole container).
Pour the rice flour, sugar and water in a bowl and mix well until it has dissolved completely.
Cover with plastic wrap and heat it on high heat in the microwave for 1 minute. Take it out and stir carefully with a spatula. Cover again and cook for 1 more minute at high heat. Stir again with the spatula and cook for 1 more minute. (Total 3 minutes).
Cover the work surface, and your hands, with corn starch (it should be abundant) and transfer the cooked mochi. Cover it completely with more corn starch and roll it until flat (about 2 mm thick).
Cut circles out of the dough using a cookie cutter. Pile the circles on top of each other, separating them with plastic wrap so they don’t stick (add more cornstarch if needed). You should get approximately 10 circles in total. We used a cutter that had a diameter of 11 cm (4.5 inches).
Scoop an ice cream portion out (There isn’t an exact amount. You can use a spoon or cookie scoop to scoop the amount that fits into the mochi dough circle.) and place it over one circle. Close the circle with the help of the plastic wrap and place it on a tray. Repeat for the rest of them.
Freeze for 30 more minutes. Remove plastic wrap and serve.