1. Heat oven to 325°F. Generously butter your 9-inch springform pan all the way up the sides. Dust the buttered pan with cocoa powder, tapping out any excess.

2. Combine chopped chocolate and butter pieces in a large microwave-safe bowl. Microwave in 30-second bursts, stirring well between each interval, until completely melted and smooth with no lumps. Set aside to cool slightly.

3. Separate eggs carefully, putting whites in stand mixer bowl and yolks in a separate small bowl. Start beating whites on medium speed, gradually increasing to high. As whites get foamy, slowly stream in sugar while mixer runs. Keep beating on high until you get medium stiff peaks.

4. Add egg yolks one at a time to the cooled chocolate mixture, whisking after each addition. Stir in vanilla, salt, and cocoa powder, whisking until smooth.

5. Drop large spoonfuls of whipped egg whites into chocolate mixture and gently fold them in with a rubber spatula. Keep folding until no white streaks remain, but don’t overmix.

6. Spoon batter into prepared pan and spread into an even layer. Bake for 45-50 minutes until a knife inserted in center comes out clean and edges start pulling away from pan. Let cool completely in pan – the top will crack and the center will fall.