Preheat oven to 350 degrees. Butter cake pans, line bottoms with parchment paper, and butter parchment. Dust pans and liners with cocoa, and tap out excess.Advertisement
Sift together flour, baking powder, and salt; set aside. In top of double boiler, combine butter, 1 pound bittersweet chocolate, and unsweetened chocolate; heat, stirring, until melted. Cool to room temperature.
In a large bowl, whisk eggs, espresso powder, and sugar until just combined. Add cooled chocolate mixture. Stir in the reserved dry ingredients. Fold in the remaining bittersweet chocolate.
To aid in baking the 10- and 12-inch layers of this dense cake, wrap two 1 1/2- inch-diameter round cookie cutters with aluminum foil, creating 3-inch-high tubes, and place in center of pans. Pour batter into pans (see batter amounts and baking times above), and bake. Brownies are done when a few crumbs remain on a cake tester inserted in center and removed. Cool on racks before unmolding.
Bake these brownies in 3-inch-high cake pans, one each that is 4, 6, 8, 10, and 12 inches square.