In a saucepan or microwave, melt butter and chopped chocolate until smooth. Let cool slightly.
Whisk in both sugars until glossy. Add eggs one at a time, then stir in vanilla.
In a separate bowl, sift together flour, cocoa powder, and salt. Gently fold into the wet mixture.
Preheat oven to 350°F (175°C). Line a 9x13-inch pan with parchment paper. Spread batter evenly.
Bake for 28–32 minutes, until edges are set but the center is still soft.
Allow brownies to cool completely in the pan. Lift with parchment and cut into neat bars.
