In a medium microwave-safe bowl, combine glutinous rice flour and sugar, mixing well. Gradually add water while whisking until the mixture is smooth and free of lumps.

Cover the bowl with a wet paper towel or a microwave-safe plate to prevent drying out. Microwave on high for 1 minute, then remove and stir with a wet spatula. Repeat this process two more times, microwaving for 1 minute at a time, until the mixture is thick, glossy, and slightly translucent. Let it cool for 5-10 minutes.

Generously dust your work surface with cornstarch to prevent sticking. Transfer the cooled mochi mixture to this surface and cut into eight equal pieces.

Flatten each mochi piece between your palms, creating a small disc. Place a chunk of ripe banana in the center, then pinch the edges together to seal.

Serve immediately or refrigerate for about an hour for a refreshing treat.