Preheat oven to 350 degrees F (175 degrees C). Spray a 9x13-inch glass baking dish with cooking spray.
Sift together the rice flour, sugar, and baking soda; set aside. Beat eggs with evaporated milk, coconut milk, and vanilla extract. Add flour and butter; beat until well combined.
Pour into prepared pan and bake in preheated oven for 30 minutes. Allow to cool completely before cutting into small (1 1/2 inch) squares.
