01 - Preheat oven to 350°F. Line an 8-inch square baking pan with parchment paper, leaving overhang for easy removal.
02 - Whisk flour, baking powder, and salt in a medium bowl until evenly blended.
03 - Whisk melted butter, brown sugar, and granulated sugar in a large bowl until combined and glossy.
04 - Add eggs one at a time, whisking thoroughly after each. Stir in vanilla extract and black sesame paste until fully incorporated.
05 - Fold dry ingredients into wet mixture using a spatula until just combined. Avoid overmixing.
06 - Gently fold in half the toasted black sesame seeds and optional white chocolate chips.
07 - Spread batter evenly in prepared pan. Sprinkle remaining black sesame seeds on top.
08 - Bake 22-26 minutes until center is just set and toothpick inserted comes out with moist crumbs.
09 - Cool completely in pan before lifting out and cutting into squares.