Ingredients:

  • 225g (8 ounces) dark chocolate (70% cocoa or higher), finely chopped
  • 115g (1/2 cup or 1 stick) unsalted butter, cut into cubes
  • 1/4 cup (50g) granulated sugar
  • 1/4 cup (50g) packed light brown sugar
  • 1 teaspoon pure vanilla extract
  • 1/4 teaspoon kosher salt
  • 4 large eggs, separated, room temperature
  • 1/4 teaspoon cream of tartar
  • Powdered sugar (icing sugar) for dusting (optional)

Instructions:

  1. Preheat oven to 325°F (160°C). Grease the springform pan and line the bottom with parchment paper.
  2. Melt the chocolate and butter together in a double boiler or heatproof bowl set over simmering water, stirring occasionally, until smooth. Remove from heat.
  3. Whisk in granulated sugar, brown sugar, vanilla extract, and salt into the melted chocolate mixture.
  4. Whisk in the egg yolks, one at a time, until well combined.
  5. In a separate clean bowl, beat the egg whites with cream of tartar until stiff, but not dry, peaks form.
  6. Gently fold one-third of the whipped egg whites into the chocolate mixture to lighten it. Then, gently fold in the remaining egg whites until just combined. Be careful not to overmix.
  7. Pour the batter into the prepared springform pan. Bake for 30-35 minutes, or until the edges are set and the centre is slightly soft. A toothpick inserted into the centre should come out with moist crumbs attached.
  8. Let the cake cool completely in the pan on a wire rack.
  9. Carefully remove the cake from the springform pan. Dust with powdered sugar, if desired, and serve.