Preheat your oven to 350°F (177°C) and line a 9×9-inch baking pan with parchment paper.

Melt 6 tablespoons of butter, let cool slightly, then whisk in 1.25 cups of granulated sugar, 2 eggs, 2 tablespoons of culinary matcha powder, and 1 tablespoon of vanilla until smooth.

Gradually mix in half of 1.33 cups of milk, whisk until blended, then add the remaining milk and whisk to a creamy consistency.

Pour in 2.33 cups of mochiko and 1.25 teaspoons of fine sea salt; stir gently until a uniform batter forms.

Transfer batter to the lined pan and bake for 40-50 minutes until a toothpick comes out with a few moist crumbs.

Cool the brownies on a wire rack for about 30 minutes.

For the ganache, combine 6 ounces of white chocolate chips and 0.25 cups of heavy cream in a microwave-safe bowl; heat in intervals until smooth.

Sift in 1 tablespoon of matcha powder and mix until incorporated before spreading onto the cooled brownies.

Chill the brownies in the refrigerator for 45 minutes, then slice into squares to serve.