The three tablespoons of flour help this cake keep its shape during baking.
- 12 ounces bittersweet or semisweet chocolate, chopped
- 3/4 cup (1 1/2 sticks) unsalted butter, cut into pieces
- 3/4 cup sugar
- 4 large eggs
- 4 large egg yolks
- 2 teaspoons vanilla extract
- 1/2 teaspoon salt
- 3 tablespoons all-purpose flour
- Cocoa powder
Preheat oven to 350 degrees F.
Butter a 9-inch-diameter springform pan. Stir chocolate and butter in a large wide metal bowl. Set over a saucepan of simmering water until melted and smooth. Remove from heat. Cool 10 minutes, stirring occasionally.
Using an electric stand mixer and whisk attachment, beat sugar, eggs, egg yolks, vanilla, and salt in large bowl until very thick ribbon falls when attachment is lifted, about 8 minutes. Sift flour over egg mixture, then fold in. Fold egg mixture into cooled chocolate mixture. Transfer batter to prepared pan.
Bake cake until top is puffed and cracked and tester inserted into the center comes out with moist crumbs attached about 50 minutes.
Using a small knife, cut around pan sides to loosen cake. Cool cake in pan on rack (cake will fall). Remove pan sides. Transfer cake to a platter. Sift cocoa powder over the cake and serve.