In a medium bowl, mix together the mochiko, 1 cup of sugar, and water until well blended. Mix in the 2 drops of vinegar to soften. Pour into a microwave-safe dish, and loosely cover with plastic. Microwave for 8 to 10 minutes on HIGH. Remove, and let cool until cool enough to handle.
In a small bowl, combine the potato starch, 1/4 cup sugar, and salt. Turn the mochi out onto the plastic, and cut into pieces using a plastic or wooden knife. Metal knives tend to stick too much. Roll the pieces in the potato starch mixture.
