Pre-scoop the ice cream: Line a baking sheet with parchment. Scoop ice cream into 12 small balls (about 1 to 1.5 tablespoons each). Freeze until very firm, at least 1–2 hours. This step matters because soft scoops melt fast while wrapping.
Prepare your work area: Dust a tray or cutting board generously with cornstarch.
Have plastic wrap ready and a 3.5–4-inch round cutter (or a small bowl) nearby.
Mix the mochi batter: In a microwave-safe bowl, whisk the sweet rice flour, sugar, and optional dry flavorings. Add water or milk and optional vanilla/coloring. Whisk until smooth with no lumps.
Cook the mochi (microwave method): Cover the bowl loosely.
Microwave on high for 1 minute, stir thoroughly, then microwave 1 more minute. Stir again. Microwave for 30–60 seconds more until the mixture turns glossy, sticky, and slightly translucent. It should be thick and stretchy, not runny.
Alternatively, cook on the stovetop: Stir the mixture in a nonstick pan over medium heat for 6–8 minutes until thick, glossy, and stretchy.
Keep it moving to avoid scorching.
Turn out and dust: Scrape the hot mochi onto the cornstarch-dusted surface. Dust the top with more cornstarch to prevent sticking. Let it cool for 10–15 minutes until warm but not hot.
Roll the mochi sheet: Using a rolling pin dusted with cornstarch, roll the dough to about 1/8 inch thick.
If it springs back, let it rest a minute and roll again. Keep everything lightly dusted so nothing sticks.
Cut circles: Use your cutter or bowl rim to cut circles about 3.5–4 inches wide. Gather and reroll scraps, dusting as needed.
Aim for 12 circles.
Assemble quickly: Work with one circle at a time. Place a frozen ice cream scoop in the center, then pull the mochi up around it, pinching the seam shut at the top. If the dough resists, warm it slightly in your hands or trim if too thick.
Wrap and freeze: Place each sealed mochi seam-side down on a small square of plastic wrap. Twist to secure and freeze for at least 1 hour to set.
Serve: Let mochi sit at room temperature for 2–3 minutes before eating so the shell softens and the center becomes creamy.