1. Preheat the oven to 350°F and prepare an 8x8 baking pan.
2. Brown the butter until nutty, then pour over white chocolate and matcha powder.
3. Stir until smooth and let cool.
4. Beat sugars, eggs, vanilla, and salt until thick and creamy.
5. Stream in the matcha chocolate mixture while mixing.
6. Fold in sifted flour gently with a spatula.
7. Spread batter in pan and bake 20-25 minutes.
8. Remove, tap pan to release air, sprinkle flaky salt, and bake 10 minutes more.
9. Cool 20 minutes before cutting.