Preheat the oven to 350°F. If using a convection oven, reduce the temperature by 25°F. Melt the butter in the microwave or on the stovetop. Use the wrapper to grease the pan.

In a medium bowl, whisk together the mochiko, baking powder, and salt.

In a mixing bowl, stir the eggs and sugar on low speed or whisk gently by hand, avoiding too much air. Stir in the coconut milk, then the evaporated milk. Add vanilla extract and melted butter while mixing.

Pour the dry mixture into the wet mixture and stir until fully combined. Pour the batter into a greased 9 x 13-inch pan or divide between two 8 x 8-inch pans. Smooth the top and sprinkle coconut flakes if desired.

Bake for 50 to 60 minutes until the top is set and golden brown. A skewer inserted in the center should come out clean.

Allow the pan to cool on a wire rack for about 1 hour. For cleaner slices, cool for about 30 minutes, run a knife around the edges, invert onto parchment, and then flip right side up.

Cut into 24 squares, about 2 x 2 inches each.