Mix mochiko with water and sugar in a microwave-safe glass.

Cover bowl with plastic wrap and cook the rice flour mixture in the microwave for 2 minutes. Stir the mixture and heat it again int he microwave for another 15-30 seconds.

Dust work surface with cornstarch.

While the mochi is still hot from microwave, begin rolling balls the size of about 2 tbs.

Flatten the mochi ball and fill with Nutella in the center. Pinch the mochi until the paste is completely covered.

Sprinkle with additional cornstarch and place mochi seam side down in a paper muffin liner to prevent sticking.

Repeat until all the mochi is done.