Preheat your oven to 325°F (163°C) and grease a 9-inch springform pan. Dust the pan with cocoa powder.

In a microwave-safe bowl, combine chopped chocolate and unsalted butter. Microwave in 30-second intervals, stirring until smooth.

In a stand mixer, beat egg whites on medium-high speed, gradually adding sugar until medium-stiff peaks form.

Gently add egg yolks to the chocolate mixture, whisking in vanilla extract, salt, and cocoa powder.

Fold the whipped egg whites into the chocolate mixture gently, until no white streaks remain.

Pour the batter into the prepared pan and smooth the top with a spatula.

Bake for 45 to 50 minutes, checking for doneness with a knife.

Let the cake cool in the pan on a wire rack for 30-40 minutes before removing the sides.