In a microwave-safe bowl, combine glutinous rice flour, sugar, cornstarch, and banana milk.
Cover the bowl with plastic wrap, ensuring to poke a few holes for steam to escape.
Microwave the mixture for 2-3 minutes until it forms a smooth, elastic dough.
Add 1 tbsp of butter to the hot dough and allow it to melt, then mix well until fully incorporated
Let the dough cool until it’s safe to handle.
Dust a clean work surface with cornstarch to prevent sticking.
Transfer the dough onto the cornstarch-dusted surface and cut it into evenly sized pieces.
Flatten each piece with a rolling pin and place a small amount of the prepared filling in the center.
Carefully seal the edges of the dough to encase the filling.
Repeat the process with the remaining dough and filling.
Serve your delicious Banana Milk Mochi immediately or refrigerate for later enjoyment.