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