• Line an 8×8-inch (20×20 cm) baking dish with parchment paper and set aside.
• In a large microwave-safe bowl, combine the mochiko flour, sugar, and cocoa powder, and then whisk in the milk.
• Cover the bowl with plastic wrap and microwave on HIGH for 2 minutes. Then add in the butter and whisk the batter, scraping the sides of the bowl until the butter melts and the batter comes together.
• Microwave the mochi mixture again at 30-second intervals until it holds together in the center of the bowl but is still soft and spreadable.
• Transfer the batter to the prepared tray, cover, and refrigerate until completely cold, about 2 hours.
• Scoop sixteen 1½ tablespoon-sized balls of ice cream onto a small baking tray lined with parchment. Place in the freezer until ready to use.

Assembling the Chocolate Mochi Ice Cream

• Cut the cold dough into 16 squares by cutting 4 x 4 lines.
• Generously dust one ball with cornstarch and roll it between 2 pieces of plastic wrap into a roughly 3×3-inch (7½ x 7½cm) square. Remove the top piece of plastic wrap and set aside.
• Working quickly, place a ball of ice cream in the center of the mochi square and use the bottom piece of plastic wrap to help you handle the mochi and wrap it around the ice cream (see step-by-step instructions in the video below).
• Twist the plastic wrap around the assembled mochi ice cream ball to help it hold its shape, flatten it slightly into a dome shape, and keeping it wrapped in plastic, return it to the freezer. Repeat with the remaining mochi and ice cream balls. (You can reuse the top piece of plastic wrap for all of the mochi.)
• Let the mochi freeze for at least two hours before eating.