Pre-heat oven to 350 degrees Fahrenheit.
Butter or grease a 9"x13" baking pan.
In a large bowl, mix dry ingredients together: Mochiko flour, sugar, baking powder, salt.
In a separate medium bowl, start mixing some wet ingredients together: milk, eggs, vanilla extract.
Slowly pour the wet ingredients into the dry ingredients, gently stirring and mixing as you pour.
Add coconut milk next, and then melted butter, gently stirring and mixing as you pour.
Mix well until there are no lumps and the butter mochi batter has a smooth, even consistency.
Pour the batter into the prepared 9"x13" baking pan.
Tap the pan against a tabletop or countertop a couple of times to remove air bubbles.Optional: sprinkle some coconut flakes on top of the mixture after tapping. Bake at 350 degrees Fahrenheit for 60 mins on middle oven rack.
Remove and let cool completely on wire rack to room temperature before cutting into 2-inch pieces and servingOptional: Top with powdered sugar, whipped cream, or your favorite fruits!