01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - Toast black sesame seeds in a dry skillet over medium heat for 2-3 minutes until fragrant. Cool slightly, then grind 1/3 cup in a spice grinder until fine. Reserve 2 tablespoons whole seeds for topping.
03 - In a medium bowl, whisk together the flour, baking powder, and salt until well blended.
04 - In a large bowl, whisk the melted butter and brown sugar until smooth. Add the egg and vanilla, whisking until well combined.
05 - Stir the ground black sesame into the wet mixture until fully incorporated and the batter is uniformly gray.
06 - Add the dry ingredients to the wet mixture and fold together gently until just combined. Do not overmix.
07 - Fold in the white chocolate chips until evenly distributed throughout the batter.
08 - Pour the batter into the prepared pan and smooth the top with a spatula. Sprinkle evenly with the reserved whole black sesame seeds.
09 - Bake for 22-25 minutes, or until the edges are golden and a toothpick inserted into the center comes out with a few moist crumbs.
10 - Let cool completely in the pan before lifting out using the parchment overhang. Cut into 16 squares.