Preheat oven to 350 F. Place oven rack in middle of oven. Lightly spray a 13- x 9-inch baking dish with vegetable oil spray.
In the bowl of your electric mixer, cream together the sugar and butter until well combined. Add the milk, beaten eggs, and vanilla extract; continue beating until combined. Add the baking powder and the sweet rice flour (Mochiko) until batter is combined and smooth.
Pour the mochi batter into the prepared baking dish.
Bake approximately 1 hour (60 minutes) until the top of the cake is golden and cake begins to pull away from sides of pan. Remove from oven and let cool on a cooking rack.
Cut into small squares to serve.
* The Hawaiian versions of this cake usually use coconut milk.
** Mochiko is available in Asian stores and some large supermarkets. It comes in 1-pound (16 ounce) boxes (see photo on right).
Butter Mochi Cake Recipe: https://whatscookingamerica.net/cake/buttermochicake.htm