In a large mixing bowl, combine glutinous rice flour, cornstarch, and granulated sugar. Gradually pour in milk while whisking until smooth.

Pour the mixture into a heatproof dish and steam over medium heat for about 20 minutes until the dough is firm and translucent.

Carefully remove the dough from the steamer, let cool for a minute. Add oil or melted butter and knead until smooth.

Divide the dough into small pieces, flatten them, place a piece of banana in the center, and pinch to seal.

Roll each shaped mochi in coconut flakes to coat evenly.

Optionally dust with powdered sugar or drizzle with melted dark chocolate before serving.