Instant childhood memories.
Yields 24 two-inch-square brownies
1-1/4 cups plain cake flour (5 ounces)
(If you don’t have cake flour, Start with one level cup of AP flour, remove two tablespoons of the flour, and add two tablespoons of cornstarch or arrowroot powder back in. Then sift the mixture together to be sure the ingredients are well distributed.)
1/2 teaspoon sea salt
3/4 teaspoon baking powder
6 ounces Guittard Unsweetened Chocolate Gourmet Baking Bar, chopped fine
12 tablespoons unsalted butter (1-1/2 sticks), cut into six 1-inch pieces
2-1/4 cups sugar (15 3/4 ounces)
4 large eggs
1 tablespoon vanilla extract
Topping: 4 ounces Guittard Unsweetened Chocolate Gourmet Baking Bar, chopped into chocolate-chip-sized chunks
Adjust oven rack to middle position; heat oven to 325 degrees. Cut 18-inch length foil and fold lengthwise to 8-inch width. Fit foil into length of 13- by 9-inch baking dish, pushing it into corners and up sides of pan; allow excess to overhang pan edges. Cut 14-inch length foil and, if using extra-wide foil, fold lengthwise to 12-inch width; fit into width of baking pan in same manner, perpendicular to first sheet. Spray foil-lined pan with nonstick cooking spray.
Whisk to combine flour, salt, and baking powder in medium bowl; set aside.
Melt chocolate and butter in large heatproof bowl set over saucepan of almost-simmering water, stirring occasionally, until smooth. (Alternatively, in microwave, heat butter and chocolate in large microwave-safe bowl on high for 45 seconds, then stir and heat for 30 seconds more. Stir again, and, if necessary, repeat in 15-second increments; do not let chocolate burn.) When chocolate mixture is completely smooth, remove bowl from saucepan and gradually whisk in sugar. Add eggs one at time, whisking after each addition until thoroughly combined. Whisk in vanilla. Add flour mixture in three additions, folding with rubber spatula until batter is completely smooth and homogeneous.
Transfer batter to prepared pan; using spatula, spread batter into corners of pan and smooth surface. Sprinkle 4 ounces of chopped chocolate evenly over batter and bake until toothpick or wooden skewer inserted into center of brownies comes out with few moist crumbs attached, 30 to 35 minutes.
Be sure to test for doneness before removing the brownies from the oven. If underbaked (the toothpick has batter clinging to it), the texture of the brownies will be dense and gummy; if overbaked (the toothpick comes out completely clean), the brownies will be dry and cakey.
Cool on wire rack to room temperature, about 2 hours, then remove brownies from pan by lifting foil overhang. Cut brownies into 2-inch squares and serve. (Store leftovers in airtight container at room temperature up to 3 days.)