Preheat oven to 350°F. Grease a 9x9 inch baking pan or line it with parchment paper.
In a bowl, whisk together butter, sugar, eggs, 2 tablespoons matcha powder, and vanilla extract until smooth.
Add about half of the milk and whisk to combine. Add the remaining milk and whisk until fully incorporated.
Whisk in the sweet rice flour and salt until you have a smooth batter.
Pour the batter into the prepared baking pan and spread evenly with a spatula. Bake for 40-50 minutes, or until a toothpick inserted into the center comes out clean.
Remove the brownies from the oven and let them cool in the pan on a wire rack for about 30 minutes.
Meanwhile, prepare the matcha ganache.
Place the white chocolate chips and heavy cream in a microwave-safe bowl. Microwave for 45 seconds, then stir with a silicone spatula.
If the chocolate is not completely melted, microwave in 10-second intervals, stirring until smooth.
Sift in the matcha powder and stir well to combine.
Pour the matcha ganache over the brownies and spread evenly with a spatula.
Refrigerate for about 45 minutes, or until the ganache is set.
Remove the matcha mochi brownies from the pan and cut into 9 pieces.
