Get a large bowl out because you are going to need it. Mix together 4 cups of mochiko (FYI, this is more than one box), 2 1/2 cups sugar, 3 tsp baking powder, 4 cups milk, 4 eggs, and 2 tsp vanilla. Feel free to sub a cup of coconut milk for regular milk. Add 1 block of melted butter to the mixture.
Bake in a greased 9x13 pan at 325 degrees for 1 hour and 30 minutes or until edges are brown. You may want to put a cookie sheet under the pan to catch any butter drippings. My oven is still waiting to be cleaned up.
Cool. Cut. Eat. Enjoy! Thanks Susan F. for passing on this awesome butter mochi recipe!