2/3 cup unsifted bleached cake flour
1/2 teaspoon baking powder
1/2 teaspoon salt
1/2 cup plus 2 tablespoon unsweetened alkalized cocoa powder
1 pound (4 sticks) unsalted butter, melted and cooled to tepid
10 ounces unsweetened chocolate, melted and cooled to tepid
6 ounces bittersweet chocolate, melted and cooled to tepid
10 large eggs
4 cups superfine sugar (I used regular granulated sugar and it was fine)
4 teaspoons vanilla extract
- Preheat oven to 325 degrees F. Line a 9 x 13 pan with foil and lightly spray with nonstick cooking spray.
- Sift together the all-purpose flour, cake flour, baking powder, salt and cocoa powder.
- Whisk together the melted butter and melted chocolates in a medium-size mixing bowl until smooth.
- In a large bowl, whisk the eggs just to mix. Add the sugar and beat for 1 minute. Blend in the melted butter-chocolate mixture and the vanilla extract.
- Whisk in the flour mixture, mixing slowly to form a batter, scraping down the sides of the mixing bowl with a rubber spatula to keep the batter even-textured.
- Pour the batter into the prepared pan and smooth the top with a metal spatula. Bake for 36 to 39 minutes, or until just set and a toothpick inserted near the center comes out with a few moist crumbs. Cool completely before cutting and serving.