Step 1: Preheat your oven to 350°F (175°C) for even baking.
Step 2: Line a 9x9-inch baking pan with parchment paper, leaving overhang for easy removal.
Step 3: In a medium saucepan over low heat, melt the chopped semisweet and unsweetened chocolate with the butter until smooth. Remove from heat and cool slightly.
Step 4: Whisk in the cocoa powder into the cooled chocolate mixture until fully combined.
Step 5: In a separate bowl, whisk together the eggs, granulated sugar, vanilla extract, and salt until well blended.
Step 6: Pour the chocolate mixture into the egg mixture and stir gently until just combined. Gradually fold in the flour, taking care not to overmix.
Step 7: Pour the batter into the prepared pan, spreading it evenly. Bake for 20-25 minutes, or until a toothpick comes out with a few moist crumbs.
Step 8: Allow the brownies to cool in the pan for 15 minutes, then lift out using the parchment and cool completely on a wire rack before cutting into squares.
