01 - Set oven to 350°F. Grease a 9x9-inch baking pan and line with parchment paper.
02 - Whisk together flour, cocoa powder, salt, and baking powder in a medium bowl. Set aside.
03 - In a large bowl, whisk melted butter with granulated and brown sugar until smooth.
04 - Add eggs individually to the sugar mixture, whisking thoroughly after each addition, then stir in vanilla extract.
05 - Gently melt dark chocolate using a microwave or double boiler, let cool slightly, then whisk into the wet mixture.
06 - Fold dry ingredients into wet mixture with a spatula until just combined, avoiding overmixing.
07 - Spread batter evenly in the prepared baking pan.
08 - Bake for 28 to 32 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
09 - Allow brownies to cool completely in the pan on a wire rack before cutting into squares.