200 gms semisweet baking chocolate, broken into pieces
3/4 cup unsalted butter
5 eggs, separated
1 tsp vanilla
1/3 cup sugar
2 tbsp unsweetened cocoa powder
1/8 tsp salt
For cake, preheat oven to 175 degrees celsius. Grease 9-inch springform pan. Heat chocolate and butter in medium saucepan over low heat until melted, stirring frequently.
Remove from heat; whisk in egg yolks and vanilla. Blend in sugar, 2 tablespoons cocoa and salt
Beat egg whites to soft peaks in large bowl. Stir about one fourth of egg whites into chocolate mixture. Fold chocolate mixture into remaining egg whites.
Spread batter evenly in prepared pan. Bake about 30 minutes or until toothpick inserted in center comes out clean and edge of cake begins to pull away from side of pan. Cool cake in pan on wire rack 2 to 3 minutes; carefully loosen edge of cake with sharp knife and remove side of pan.
Cool cake completely. Cover and refrigerate overnight or up to 3 days, or wrap well and freeze up to 3 months.