In a mixing bowl, whisk together the mochiko, sugar, and water until you have a smooth batter without lumps.

Transfer the mochi mixture to a microwave-safe bowl, cover, and cook in the microwave for 1 minute. Stir, then return to microwave for another minute; repeat until thickened and slightly translucent, about 4-5 minutes total.

After cooking, stir in the vanilla extract until evenly incorporated.

Dust a clean surface with cornstarch, pour the mochi dough onto it, and let cool until manageable.

Divide the dough into 6 pieces, flatten each, place a spoonful of crushed Oreo in the center, fold edges to create a ball, and roll gently.

Dust each shaped mochi with cornstarch, place on a plate, and chill in the refrigerator for at least 30 minutes before serving.