Step 1: Prepare Matcha Ice Cream : Whisk matcha powder with sugar in a small bowl. Heat milk and cream over medium heat until warm, then whisk in matcha-sugar mixture. In a separate bowl, beat egg yolks. Slowly temper yolks by adding some warm milk mixture, then combine fully. Cook over low heat, stirring until custard thickens (coat the back of a spoon). Strain, cool, and freeze in a container for at least 2–3 hours until firm.

Step 2: Prepare Mochi Dough : In a microwave-safe bowl, mix glutinous rice flour, sugar, and water until smooth. Cover loosely and microwave for 2 minutes. Stir, then microwave another 1–2 minutes until dough is sticky and slightly translucent. Dust a surface with cornstarch and roll out mochi dough to ~¼ inch thickness.

Step 3: Assemble Mochi Ice Cream : Cut mochi dough into circles (~3 inches in diameter). Scoop small balls of frozen matcha ice cream. Place ice cream in the center of a mochi circle, pinch edges together to seal. Roll lightly in cornstarch to prevent sticking. Freeze assembled mochi for at least 1–2 hours before serving.