Place the cake flour, the warabi starch, and the sugar in a bowl. Add the water a little at time, and mix well so as not to leave lumps.
Strain the mixture into the cake pan through a strainer, and cover with plastic wrap with a little space open at one side of the cake pan.
Microwave at 600 W for 5.5 to 6 minutes. Remove from the microwave and unwrap. Then place the unwrapped plastic wrap back on top of the uiro and let cool.
Once the uiro has cooled, chill in the fridge. When it has chilled completely, remove from the cake pan and cut. The uiro is ready to be served.
The uiro is really soft just after heating, but it will be springy when chilled completely! You can feel how springy and textured it is when you shake it.
You can substitute warabi starch with cake flour, but the taste and texture will be very different. So, I strongly recommend using warabi starch as well!
Story Behind this Recipe
I love uiro! I've eaten so many kinds of uiro, but I love the one in Yamaguchi prefecture the most. Did you know the texture differs depending on the geographical location in Japan?
Double the amount of ingredients if you use an 18 cm Pyrex pound cake pan. Also set the cooking time a little longer when microwaving. Keep your eye on it and microwave a bit at a time to prevent any over-cooking.