Preheat oven to 350° F. Grease a 9×13 pan, preferably metal to further reduce sticking. Mix dry ingredients (mochiko, baking powder and sugar) in a large bowl. In a separate bowl, mix wet ingredients (coconut milk, water and vanilla extract). Make a well in the dry ingredients, pour a small portion of the wet ingredients into the well, and fold in. Continue until batter has the consistency of pancake batter.
Pour mixture into pan, cover with foil and bake for one hour. Allow to cool for 4 hours, then cut into pieces and dust with powdered sugar.