1 1/3 cups coarsely chopped 70% to 85% dark chocolate
1 cup unsalted butter
6 large eggs, separated, room temperature
1 cup granulated sugar
Preheat the oven to 350°F. Grease a 23 centimeter springform pan with butter or non-stick cooking spray and dust with cocoa powder.
In a medium saucepan, bring three centimeters or so of water to a simmer.
Combine the chocolate and butter in a large heatproof bowl and place over the simmering water. Stir until melted and smooth. Remove the bowl from the pot and allow to cool to room temperature.
In the bowl of a stand mixer fitted with the whisk attachment, whisk the egg yolks with 1/2 cup of the sugar on medium speed until they reach the ribbon stage. Transfer to medium bowl.
Thoroughly clean and dry the mixer bowl and the whisk attachment, then place both back on the mixer. Add the egg whites to the bowl and whisk on medium-high speed while adding the remaining 1/2 cup of sugar in a very slow, steady stream. Continue whisking until soft peaks form.
Add the egg yolk mixture and half of the egg whites to the room-temperature chocolate mixture and gently fold until smooth and combined. Do not overmix the batter or it will deflate. Gently but thoroughly fold in the remaining egg whites. Spoon the batter into prepared pan.
Bake for 30 minutes or until a toothpick inserted in the centre comes out clean. (This batter is very fragile, so do not rotate the pan during baking.) Allow the torte to cool completely in the pan on a wire rack. Once cooled, gently remove the sides of the pan. The torte can be stored in an airtight container at room temperature for up to three days.