Step 1

Preheat oven to 350°F. Line a 13- x 9-inch metal baking pan with parchment paper, leaving 2 inches of overhang on all sides. Lightly coat parchment paper with cooking spray. Sift together flour, cocoa, and salt in a small bowl; set aside.

Step 2

Melt 1 cup chocolate wafers over a double boiler or in the microwave, stirring often, until smooth. Combine granulated sugar, melted butter, brown sugar, eggs, and vanilla in bowl of a stand mixer. Beat on medium-high speed until frothy and light caramel in color, about 1 minute.

Step 3

With mixer running on low speed, slowly pour melted chocolate into egg mixture. Fold in flour mixture until incorporated. Transfer batter to prepared pan, and smooth top. Roughly chop remaining 1/3 cup chocolate wafers, and sprinkle over top of batter. Bake in preheated oven until a wooden pick inserted in center comes out clean, 18 to 20 minutes. Cool brownies in pan on a wire rack at least 2 hours. Using parchment, remove brownies from pan. Cut into 20 rectangles.