Preheat oven to 350 degrees F. Line a 9 inch square pan with nonstick foil or line with regular foil and spray foil with cooking spray.
Place butter and cut-up chocolate in a microwave-safe bowl; Microwave on high for 30 seconds. Stir. Continue microwaving and stirring every 30 seconds until mixture is melted. Set aside and let cool for 5 minutes.In a second bowl, beat sugar, vanilla, and eggs with electric mixer on high for a full 5 minutes. Stir melted chocolate mixture into egg mixture. When chocolate is incorporated, stir in flour.
Pour into pan and bake for 30 minutes. Cool on a wire rack. For a cleaner cut, chill the brownies before cutting.When cool, grasp foil, lift from pan, place on a cutting board and cut brownies into big squares.
