Soak the glutinous rice in water overnight.
Drain the rice and place it in a steamer lined with cheesecloth.
Steam the rice for about 30 minutes until fully cooked and sticky.
Transfer the steamed rice to a large bowl.
Add sugar and mix well while the rice is still hot.
Use a pestle or your hands to pound the rice until smooth and stretchy.
Dust your work surface and hands with cornstarch to prevent sticking.
Divide the mochi dough into equal portions.
Flatten each portion and place a small amount of filling in the center.
Seal the mochi by folding the edges over the filling and shaping it into a ball.
Coat the finished mochi in cornstarch to prevent sticking.