• Preheat the oven 350°F (177°C). Line an 8x8-inch baking dish with parchment paper.
• Combine the flour, sugar, and matcha powder in a large bowl.
• Beat melted butter, eggs, and vanilla with an electric mixer in a second bowl. Stir in the dry ingredients.
• Pour the batter into the baking dish. Use the back of a spoon or spatula to spread the batter evenly.
• Bake for 35-40 minutes until you can prick the center with a toothpick and it comes out clean. Remove from the oven, place on a cooling rack, and leave to cool completely in the pan.
  Lift the parchment paper and brownies out of the pan. Decorate with optional frosting. Cut into 9 squares.

For the frosting:

• Prepare the frosting while the brownies bake. Melt the white chocolate in a double boiler. Cool slightly.
• Beat the butter in a stand mixer until fluffy. Sift in the powdered sugar and beat again.
• Add the white chocolate, vanilla, and milk. Mix well to combine. 
• Set aside until the brownies are cool enough to cut. Remove the brownies from the baking dish and pipe frosting over the brownies as shown in the photographs or spread in a thin, uniform layer. Then, cut to serve.