12 tablespoons (1 ½ sticks) unsalted butter, cut into small cubes
6 ounces bittersweet chocolate, chopped
½ cup unsweetened Dutch-process cocoa
¾ cup granulated sugar
4 large eggs
¼ teaspoon kosher salt
1 tablespoon vanilla extract
Confectioners’ sugar for garnish
Preheat oven to 325 degrees. Butter an 8 inch round cake pan and line with parchment paper. Lightly butter the paper and dust the sides of the pan with cocoa powder. Shake out access powder and set aside.
Place chocolate in a bowl over barely simmering water and allow to melt.
Combine butter and sugar in the bowl of an electric stand mixer fitted with the paddle attachment and cream until light and fluffy. Sift cocoa onto a piece of parchment paper. Add salt and set aside.
Separate the eggs. Place the whites in the bowl of a stand mixer and whip until soft peaks form. Place the yolks into a separate bowl and stir in vanilla extract.
Add melted chocolate into the butter mixture, mix until incorporated. Add in the cocoa and salt. Then add the egg yolks with vanilla extract. Mix until combined. Remove bowl from stand mixer, using a rubber spatula, carefully fold in the egg whites.
Scrap batter into prepared pan, level top and tap the pan lightly. Place pan in a baking tray in the middle rack of the preheated oven. Pour water into the tray, careful not to spill into the cake batter. Bake for approximately 1 hr. Remove cake to a cooling rack. Allow to cool completely. Remove cake from pan and garnish.
Optional finishes: Dust with coco powder, glaze with chocolate glaze.