Whisk mochiko, cornstarch, baking powder, and salt together until combined. Set aside.
Add milk, sugar, egg, and vegetable shortening In another bowl, and whisk together until slightly frothy.
Sift your flour mixture directly into the bowl with your wet ingredients.
Mix flour into wet ingredients until the ingredients are incorporated, and the batter is smooth with no lumps. Set aside.
In a small bowl, mix 3 tablespoons of powdered sugar, 1 tablespoon of milk, and 1 drop of any food coloring of your choice to create the frosting. Duplicate this process for as many colors of frosting as you want!
Fill a piping bag with some of your batter and pipe quarter-sized dollops in a circle onto a small piece of parchment paper to create your donut. You can trace a circle on a separate sheet of paper to place underneath the parchment as a stencil on which to base your donut.
Carefully lift the parchment paper with the donut and place it into 3 or 4 inches of boiling vegetable oil to deep fry the donut.
Remove the parchment and the donut once it looks golden brown and has a crispy texture - approximately 3-5 minutes. Set aside to cool and repeat steps 6-8 for as many donuts as possible.
Once your donuts have cooled, dip them face down in the icing and then place them right side up on a rack to dry. As the icing cools, it will turn into more of a glaze.
Serve and enjoy!
Video
Notes
You can also bake your donuts in the oven at 350F for 10-12 minutes
Mochi donuts have a chewy texture because of the mochiko. The dough will be stickier and denser than traditional donut dough.
Letting your mochi donuts cool before dipping them in the icing is important. Otherwise, it will melt right off of the donut.