Ingredients
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Cooking spray
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2 tsp unsweetened cocoa powder, plus more for dusting
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2 (4 oz) bittersweet chocolate baking bars, coarsely chopped
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3/4 cup (1 1/2 sticks) unsalted butter, cut into 1/2-inch pieces
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6 large egg yolks
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3/4 cup packed dark brown sugar
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2 tsp vanilla extract
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1/2 tsp salt
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3 large egg whites
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4 tsp granulated sugar
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Whipped cream, to serve (optional)
Steps
1
Arrange a rack in center of oven and preheat to 350°F. Coat a 9-inch cake pan or springform pan with the cooking spray. Dust with the cocoa powder, coating the bottom and sides of pan. Gently tap out any excess cocoa powder.
2
In a large microwave-safe bowl, microwave the chocolate and butter on high, in 30-sec. intervals, until melted, stirring occasionally. Whisk until smooth. Let cool slightly.
3
Using a hand mixer or stand mixer fitted with a whisk attachment, beat the egg yolks and brown sugar on medium speed 3 min., until pale and thick. Beat in the vanilla and salt. Transfer egg yolk mixture to bowl of chocolate and stir to combine. Add the cocoa powder and stir to combine. Clean mixing bowl and whisk attachment very well.
4
In cleaned bowl, beat the egg whites on medium speed 2 min., until thickened. With mixer running, add the granulated sugar, 1 tsp at a time. Increase speed to medium-high and beat 1–2 min., until soft peaks form.
5
Add about one-third of egg white mixture to chocolate mixture and fold until just combined. Repeat with remaining egg white mixture, adding in 2 batches. Transfer to prepared cake pan. Bake 35–40 min., until cake is puffed and beginning to crack in a few spots. Remove from oven and let cool slightly. Serve with whipped cream, if desired.
