01 - Preheat the oven to 350°F. Line a 9x9 inch 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.
03 - In a large bowl, whisk melted butter and sugar until glossy. Add eggs one at a time, whisking well after each addition. Stir in vanilla extract.
04 - Gently fold the dry ingredients into the wet mixture with a spatula until just combined, avoiding overmixing.
05 - Fold in chocolate chips or chopped chocolate evenly.
06 - Pour the batter into the prepared pan and smooth the surface.
07 - Bake for 28 to 32 minutes, or until a toothpick inserted near the center emerges with moist crumbs.
08 - Allow to cool completely in the pan before lifting out using parchment overhang and cutting into 12 squares.