Mochiko is a Japanese rice flour that can be found in Asian sections of the market. Mochiko gives a nice chew perfect for these donuts.
In a large bowl mix together the mochiko, flour, vanilla sugar, eggs, milk, baking powder and vanilla. Set aside.
Heat the oil in a large skillet or home fryer
Drop by the tablespoon into the hot oil. They will expand a lot. Also the mochiko makes the batter very pull-y and sticky so try your best to keep it formed into nice round shapes.
Once the dough pops up and floats, fry until golden brown, a few minutes on each side.
Drain them on a wire rack
While still hot, roll the donuts in the cinnamon sugar mixture.
The only thing you will have to make ahead is the vanilla sugar. Scrape and bury a vanilla bean into two cups of sugar. Keep in an airtight container until you are ready to use.