Preheat oven to 350°F. Butter and line a 9″x9″ pan with parchment paper and set aside.
In a large microwave-safe bowl, combine butter and sugar. Microwave for 30 seconds at a time until the butter has melted. Remove and stir with a whisk or use a hand blender. I use the latter. Mix until the batter has a glossy finish.
Add eggs one at a time, whisking/mixing in between each addition.
Add cocoa powder, matcha, salt, and vanilla extract. Fold in flour until just combined. Pour mixture into prepared baking pan and bake for roughly 50 minutes, testing for doneness by inserting a toothpick in the center of the brownies beginning at 40 minutes.
Cool completely before cutting as these brownies are very fudgy and will fall apart if you try to cut while hot. Be patient, it's worth it!