In a mixing bowl, whisk together glutinous rice flour, cornstarch, cocoa powder, and white sugar until well combined. Gradually stir in milk and corn oil, mixing until the batter is smooth and free of lumps.

Pour the combined mixture through a fine sieve into a non-stick pot. Use a spatula to press any remaining bits through the sieve.

Place the pot over low heat and stir the batter continuously with a spatula for about 10 to 15 minutes until it thickens and becomes glossy.

Once thickened, transfer the mochi dough onto a cornstarch-dusted surface. Allow it to cool for about 5 minutes.

Divide the soft mochi dough into equal portions and roll each piece to create smooth balls.

Crush the Oreo cookies into fine crumbs and roll the mochi balls in the Oreo crumbs until thoroughly coated.

Refrigerate the coated Oreo Mochi for about 30 minutes before serving.