Directions

1. Preheat oven to 350°F.
2. Butter a 9″ springform pan. Line bottom of pan with parchment paper, then butter the paper. To prevent any leaking, wrap the outside of the pan with aluminum foil.
3. In a medium saucepan over low heat, stir chocolate and butter until melted and smooth. Remove from heat and cool to lukewarm.
4. Beat egg yolks and half (6 tbsp) the sugar in a large bowl until thick and pale, about 3 minutes. Fold in cooled chocolate, and vanilla extract.
5. In a clean, dry bowl, with a whisk attachment, beat egg whites until soft peaks form. Gradually add remaining (6 tbsp) sugar until medium-firm peaks form. Do not overbeat. Fold whites into the chocolate mixture in 3 additions. Pour batter into prepared pan.
6. Bake cake on middle rack of oven until puffed and cracked, about 50 minutes. Cool cake in pan on a rack. The cake will fall. Gently press down on top to make an evenly thick cake. Cut around the sides of the pan to loosen the cake. Remove the sides. Invert onto cake plate, and peel off parchment paper.
7. To make the Glaze: In a medium saucepan bring whipping cream and corn syrup to a simmer. Remove from heat and add chocolate, whisking until melted and smooth. Pour glaze over cake, smoothing the top with a knife if desired. Can be made up to 2 days ahead, covered and refrigerated, or 1 week ahead and frozen without the glaze. Serve at room temperature, with whipped cream and berries, if desired.