In a large mixing bowl, combine glutinous rice flour, cornstarch, cocoa powder, and white sugar. Gradually stir in milk and corn oil until smooth.

Strain the batter through a fine sieve into a non-stick pot.

Cook over low to medium heat, stirring continuously for 8-10 minutes until thickened.

Transfer the warm mochi dough onto a cornstarch-dusted surface and knead for 5 minutes.

Divide the dough into pieces and roll them into balls.

Crush Oreo cookies into fine crumbs, then roll mochi balls in the crumbs to coat.