In a mixing bowl, whisk together 1 cup of mochiko and 1/4 cup of sugar until well-blended. Gradually add 3/4 cup of water while stirring to form a smooth batter.

Transfer the mochi batter to a microwave-safe bowl and cover it. Microwave on high for 1 minute, then stir. Repeat until thick and slightly translucent, about 4-5 minutes total.

Stir in 1/2 teaspoon of vanilla extract until fully incorporated for enhanced flavor.

Dust a clean surface with cornstarch, pour the warm mochi dough onto it, and allow to cool for about 10-15 minutes.

Divide the mochi dough into 6 equal pieces. Flatten each into a disc, place crushed Oreos in the center, and seal well.

Dust each shaped mochi with cornstarch, place on a plate, and refrigerate for at least 30 minutes.