01 - Preheat the oven to 350°F. Line an 8-inch square baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a medium bowl, whisk together flour, cocoa powder, baking powder, and salt until well blended. Set aside.
03 - In a large mixing bowl, combine melted butter, sugar, and black sesame paste. Whisk until smooth and glossy.
04 - Add eggs one at a time, whisking thoroughly after each addition. Stir in vanilla extract.
05 - Fold the dry ingredients into the wet mixture using a spatula, mixing until just combined. Do not overmix.
06 - Gently fold in the chopped dark chocolate until evenly distributed throughout the batter.
07 - Pour the batter into the prepared pan and smooth the top evenly. Sprinkle black sesame seeds over the surface if desired.
08 - Bake for 28-32 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
09 - Let cool completely in the pan before lifting out using the parchment overhang. Slice into squares.