5 oz. semisweet or bittersweet chocolate, chopped
2 oz. unsweetened chocolate, chopped
8 T (1 stick) unsalted butter, cut into quarters
3 T cocoa powder
3 large eggs
1 1/4 cups sugar
2 tsp vanilla extract
1/2 tsp salt
1 cup (5 oz.) unbleached all-purpose flour
1. Adjust an oven rack to the lower-middle position and heat oven to 350. Spray an 8-inch square baking pan with nonstick cooking spray. Fold two 16-inch pieces of foil or parchment paper lengthwise to measure 8 inches wide. Fit one sheet in the bottom of the greased pan, pushing it into the corners and up the sides of the pan. Fit the second sheet in the pan in the same manner, perpendicular to the first sheet. Spray the sheets with nonstick cooking spray.
2. In a medium heatproof bowl set over a pan of almost-simmering water, melt the chocolate and butter, stirring occasionally until smooth. Whisk in the cocoa until smooth. Set aside to cool.
3. Whisk together the eggs, sugar, vanilla and salt in a medium bowl until combined, about 15 seconds. Whisk the warm chocolate mixture into the egg mixture; then stir in the flour with a wooden spoon until just combined. Pour the mixture into the prepared pan, spread into the corners, and level the surface with a rubber spatula. Bake until slightly puffed and a toothpick inserted in the center comes out with a small amount of sticky crumbs clinging to it, 35 to 40 minutes. Cool on a wire rack to room temperature, about 2 hours. Remove the brownies from the pan using the foil or parchment handles and transfer to a cutting board. Cut into squares. (Do not cut until ready to serve; uncut brownies can be wrapped in plastic and refrigerated up to 5 days) Makes 64 1-inch brownies or 16 2-inch brownies.