Preheat oven to 350 degrees F.
Mix mochiko,salt, and baking powder together.
Mix melted butter, sugar, eggs, and vanilla.
Alternate adding mochiko mixture and milk to egg mixture in 1-2 batches. Beat until batter is smooth, making sure to scrape the bottom of the bowl.
Pour into a greased 9x13" baking pan. Bake for one hour. There should be an even, light brown crust on top and an inserted toothpick should come out clean.
Let cool, cut into squares, and serve. Leftovers can be kept in the fridge but should be brought to room temperature before eating.
