In a large mixing bowl, combine glutinous rice flour, sugar, and cornstarch. Whisk until uniform.

Add cooking oil and whole milk to the dry ingredients. Mix vigorously until smooth.

Transfer the batter to a non-stick frying pan over low heat and stir continuously for about 10 minutes.

Continue stirring until the mixture becomes a thick, elastic dough, approximately 5 more minutes.

Allow the dough to cool for about 5 minutes, then gently stretch it a few times to enhance elasticity.

Once cool enough to handle, roll the dough into a log and cut it into bite-sized pieces.

Coat each piece of mochi in roasted soybean powder and serve immediately.