Preheat the oven to 350 degrees F.
Grease a 8x8 baking pan with butter and line with parchment paper. Set aside.
Make your black sesame seed powder. Toast black sesame seeds for 20-30 seconds. Pour black sesame seeds into a spice grinder or food processor. I would recommend using a spice grinder for the finest powder. Pulse until a fine powder forms. Set aside.
Heat the butter over high heat until it melts. Lower the heat to low and cook until small brown bits start to appear. Remove from the stove.
Add white chocolate to a small bowl. Pour the brown butter over the top and stir until all the chocolate melts. Let the mixture cool for 2 minutes.
In large bowl, combine granulated sugar, brown sugar, eggs, vanilla extract, and salt. Beat with a hand mixer or stand mixer until thick and creamy (5-10 minutes).
While mixing, stream in your white chocolate mixture from step 5. Whisk until a uniform batter appears.
Lastly, sift your flour and black sesame powder into the bowl. Using a spatula, gently fold both into the batter until a black batter forms. Spoon into your prepared baking pan.
Bake for 20 minutes.
Take out the brownies and slam them on the counter to get rid of some the air. Sprinkle some flaky sea salt over the top and put the brownies back in the oven. Bake for another 15-20 minutes.
Let cool for 10 minutes before serving.