3/4 cup plus 2 tablespoons dark cocoa, at least 70%
1 cup whipping cream (optional, for garnish)
Preheat oven to 375°F. Butter and parchment line 9-inch round baking pan.
Roughly chop chocolate and place in heat-resistant bowl over pan of simmering water, not directly touching water. Add butter and melt until smooth. Meanwhile, whisk eggs until slightly frothy. Remove from heat and whisk in eggs. Using rubber spatula, fold in 3/4 cup cocoa powder (reserving the 2 tablespoons aside) until just incorporated and pour into prepared pan. Bake for 25 to 30 minutes until crust on top of cake forms.
While cake is baking, pour cream and cocoa powder in large bowl to whip ingredients in later. Place in refrigerator to dissolve powder and chill bowl.
Cool for at least 10 minutes before turning upside down onto serving plate. Remove parchment paper if stuck. Whip cream and cocoa powder in chilled bowl until just stiff peaks form. Serve alongside slice of cake or frost cake with chocolate whipped cream.