Wash beans, put in a big bowl, add water, and let sit for overnight. The beans going to soak up lots of water, so add lots.
Drain beans, transfer to a big pot, cover with water, bring to a boil. When it starts to boil, turn the heat off, drain, put back into the pot, add 3-4 times of water and 1/4 teaspoon salt, let boil again, reduce heat to medieum and cook for 40-50 minutes. Take one bean out, and press with your finger, if it is crushed, it's done. Be careful with the hot bean. You don't want your beans to cook completely so they're mush.
Drain very well, mix with 3 tablespoons Sugar, and 1 teaspoon salt. With Potato mash, crush the bean and spread to a cookie sheet to cool and dry slightly. At this stage, you can freeze them, and use later.
Lightly spray the baking dish, add a half of the mashed beans, spread well and press a little bit, then add whole rice flour mixture, spread evenly, add remaining beans, and press the top slightly. Cover with foil, bake for 1 hour. If the skewer comes out clean, it's done. ^^ Cool for 20-30 minutes, inverted to a board, and slice.