- 11.5 ounces Ghirardhelli's bittersweet (not unsweetened) chocolate chips
- 3/4 cup (1 1/2 sticks) unsalted butter
- 6 large eggs, separated
- 12 tablespoons sugar
- 2 teaspoons vanilla extract
Oven preheated to 350°F. Butter 9-inch-diameter springform pan. Wrap outside of pan with foil. Stir chocolate and butter in heavy medium saucepan over low heat until melted and smooth. Remove from heat. Cool to lukewarm, stirring often.
Using electric mixer, beat egg yolks and 6 tablespoons sugar in large bowl until mixture is very thick and pale, about 3 minutes. Fold lukewarm chocolate mixture into yolk mixture, then fold in vanilla extract. Using clean dry beaters, beat egg whites in another large bowl until soft peaks form. Gradually add remaining 6 tablespoons sugar, beating until medium-firm peaks form. Fold whites into chocolate mixture in 3 additions. Pour batter into prepared pan.
Bake cake until top is puffed and cracked and tester inserted into center comes out with some moist crumbs attached, about 50 minutes. Cool cake in pan on rack (cake will fall).