Chocolate Soufflé Cake

Steps

1. Arrange a rack in center of oven and preheat to 350°F. Coat a 9” cake pan or springform pan with cooking spray. Dust with cocoa powder, evenly coating the bottom and sides of pan. Gently tap out any excess cocoa powder.
2. In a large microwave-safe bowl, microwave chocolate and butter on high, in 30-second intervals, until melted, stirring between each interval. Whisk until smooth. Let cool slightly.
3. Using a hand mixer or stand mixer fitted with a whisk attachment, beat egg yolks and brown sugar on medium speed until pale and thick, 3 minutes. Beat in vanilla and salt. Transfer egg yolk mixture to bowl of chocolate and stir to combine. Add cocoa powder and stir to combine. Clean and dry mixing bowl and whisk attachment thoroughly.
4. In clean, dry bowl, beat egg whites on medium speed until thickened, 2 minutes. With mixer running, add granulated sugar, 1 teaspoon at a time, until incorporated. Increase speed to medium-high and beat until soft peaks form, 1 to 2 minutes.
5. Add about one-third of egg white mixture to chocolate mixture and gently fold until just combined. Repeat with remaining egg white mixture, adding in 2 batches. Transfer mixture to prepared cake pan. Bake until cake is puffed and beginning to crack in a few spots, 35 to 40 minutes. Remove from oven and let cool slightly. Serve warm with whipped cream, if desired.