In a large mixing bowl, combine the sweet rice flour and sugar until well mixed.

Gradually add water, stirring continuously until you create a smooth, thick batter.

Transfer the batter to a microwave-safe dish. Cover it with plastic wrap and microwave on high for 1 minute.

Stir well and microwave for an additional minute, repeating this process until the dough becomes sticky and slightly translucent (about 3 minutes total).

Dust a clean surface with cornstarch to prevent sticking and transfer the dough onto it. Allow it to cool for a few minutes.

Divide the dough into small pieces, roughly 2 tablespoons each.

Flatten each piece in your palm and place a spoonful of Nutella in the center. Carefully wrap the dough around the filling, pinching the edges to seal it, then roll it into a ball.

Roll the finished mochi in cornstarch to keep them from sticking together and let them cool completely before serving.