5 oz. semisweet or bittersweet chocolate, chopped
2 oz. unsweetened chocolate, chopped
8 tbsp. unsalted butter, cut into quarters
3 tbsp. cocoa powder
3 large eggs
1¼ cups (8¾ oz.) sugar
2 tsp. vanilla extract
½ tsp. salt
1 cup (5 oz.) all-purpose flour
Place an oven rack in lower-middle position and preheat the oven to 350° F. Line an 8-inch square baking dish with foil and spray lightly with nonstick cooking spray; set aside.
In a heatproof bowl set over a pan of barely simmering water, melt the chocolate and butter, stirring occasionally until smooth. Whisk in the cocoa powder until smooth. Set aside to cool.
In a medium bowl, combine the eggs, sugar, vanilla and salt; whisk until combined, about 15 seconds. Whisk in the warm chocolate mixture until incorporated. Then stir in the flour with a wooden spoon until just combined. (It took me a while to get the flour evenly incorporated and I was worried it would affect the texture of the brownies, but they turned out fabulously – no need to worry.) Pour the mixture into the prepared pan and spread with a spatula to make an even layer. Bake until slightly puffed and a toothpick inserted in the center comes out with a small amount of sticky crumbs clinging to it, 35-40 minutes. Transfer the pan to a wire rack and let cool to room temperature, about 2 hours.
Remove the brownies from the pan using the foil and transfer to a cutting board. Cut into squares as desired. Store in an air-tight container.