01 - Preheat oven to 350°F. Line an 8-inch square baking pan with parchment paper, leaving overhang for easy removal.
02 - In a medium bowl, whisk together flour, baking powder, and salt until well blended.
03 - In a large bowl, whisk melted butter, brown sugar, and granulated sugar until combined and glossy.
04 - Add eggs one at a time, whisking thoroughly after each addition. Stir in vanilla extract and black sesame paste until fully incorporated and smooth.
05 - Fold dry ingredients into wet mixture using a spatula until just combined. Avoid overmixing to maintain tender texture.
06 - Gently fold in half the toasted black sesame seeds and white chocolate chips if using.
07 - Spread batter evenly in prepared pan. Sprinkle remaining black sesame seeds over surface.
08 - Bake for 22-26 minutes until center is just set and toothpick inserted comes out with a few moist crumbs.
09 - Cool completely in pan before lifting out using parchment overhang. Cut into 16 squares.