Instructions

• Preheat the oven to 350°F (175°C). Spray a 9" x 13" baking dish with cooking spray and line it with parchment paper, leaving overhang on two opposite sides for lifting.
• In a medium bowl, whisk together 1½ cups all-purpose flour, ¼ cup unsweetened cocoa powder, and 1 teaspoon kosher salt. Set aside.
• Chop 2 ounces of the semi-sweet chocolate and set aside for later.
• Place 16 tablespoons (2 sticks) unsalted butter and 10 ounces of the semi-sweet chocolate in a large microwave-safe bowl. Microwave on HIGH in 1-minute intervals, stirring between intervals, until the butter and chocolate are fully melted and smooth. (Be careful not to overheat.)
• Stir 1½ cups sugar and ½ cup dark brown sugar into the melted chocolate-butter mixture until the sugars are mostly dissolved and the mixture is smooth.
• Add the 5 large room-temperature eggs to the chocolate mixture one at a time, whisking well after each egg until fully incorporated.
• Stir in 2 teaspoons vanilla extract.
• Gently fold the flour/cocoa mixture (from step 2) into the wet mixture, stirring just until no dry streaks remain and the batter is uniform.
• Stir the chopped 2 ounces of semi-sweet chocolate into the batter.
• Pour the batter into the prepared baking dish and smooth the top with a spatula. Bake at 350°F for 30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs but not wet batter.
• Remove the pan from the oven and transfer to a wire rack to cool. If using, sprinkle up to 1 tablespoon coarse sea salt over the top while slightly warm.
• When cool enough to handle, use the parchment overhang to lift the brownies from the pan onto a cutting board. Cut into 12 bars.