In a medium microwave-safe bowl, whisk together the glutinous rice flour and sugar until combined. Gradually add the water while stirring until smooth.

Cover the bowl with a damp paper towel and microwave on high for 1 minute, stirring after each minute until thick and translucent.

Let the mochi cool for about 5-10 minutes at room temperature.

Dust a clean work surface with cornstarch and transfer the mochi onto it, sprinkling more cornstarch on top.

Cut the mochi into eight equal pieces with a cornstarch-dusted knife.

Flatten each mochi piece, place a chunk of banana in the center, and pinch the edges to seal.

Dust shaped mochi with cornstarch to prevent sticking and serve or refrigerate.

Store leftovers in an airtight container in the refrigerator for up to three days.