In a large mixing bowl, combine 1 cup of glutinous rice flour, 1/4 cup of cornstarch, 1/4 cup of cocoa powder, 1/3 cup of white sugar, 1 tablespoon of corn oil, and 1 cup of milk. Whisk thoroughly until the mixture is smooth and free of lumps.

Pour the batter through a fine sieve into a medium-sized pot to ensure a velvety texture without any clumps.

Place the pot over low heat and continuously stir the batter with a wooden spatula for 10 to 15 minutes until it thickens and pulls away from the sides.

Transfer the thickened mochi dough to a cornstarch-lined surface and let it cool for about 5 minutes.

Divide the elastic mochi dough into tablespoon-sized portions and roll each into smooth balls.

Crush Oreo cookies into fine crumbs and roll each mochi ball in the crumb mixture until fully coated.