Steps
1. In a microwave-safe bowl, mash the ripe banana until smooth.
2. Add the sweet rice flour, sugar, milk, and a pinch of salt to the mashed banana. Mix until well combined.
3. Cover the bowl with plastic wrap and microwave on high for 1 minute.
4. Stir the mixture, then microwave for another 30 seconds. Repeat until the mixture thickens and becomes sticky.
5. Dust a clean surface with cornstarch and turn the mochi mixture out onto it. Allow it to cool slightly.
6. While the mochi is cooling, melt the dark chocolate in a microwave or over a double boiler, stirring until smooth.
7. Once the mochi has cooled enough to handle, divide it into small pieces and shape them into flat disks.
8. Place a small spoonful of melted chocolate in the center of each disk and fold the mochi around the chocolate, sealing it tightly.
9. Roll the filled mochi in cornstarch to prevent sticking, then serve immediately or chill for a firmer texture.