This cake is a cross between a brownie and angel cake. It gets a lift from the egg whites alone, so no baking powder or baking soda is needed. It is light and soft- almost sponge-like. But, I think the best thing about this cake is that it is not too sweet and not too rich so you can self indulge and not feel too guilty!
3 oz bittersweet chocolate, finely chopped
½ cup plus 1/3 cup granulated sugar, divided
1/3 cup unsweetened cocoa powder
1/8 tsp salt
½ cup boiling water
3 large eggs, separated, at room temperature
½ tsp pure vanilla extract
¼ cup all-purpose flour
3 large egg whites, at room temperature
½ tsp lemon juice
2 to 3 tsp icing sugar for dusting
Preheat oven to 375°F. Line the bottom of an 8-inch springform pan with a round of parchment paper and line the inside circumference with a strip of parchment. Combine the chocolate, ¼ cup sugar, cocoa and salt in a medium bowl. Pour in the boiling water and whisk until mixture is smooth and the chocolate is completely melted. Let cool while you beat the egg yolks.
In a separate bowl, beat egg yolks with vanilla extract using an electric mixer on high speed until blended. Gradually beat in ¼ cup sugar until pale yellow and thick, about 2 minutes. Fold in chocolate mixture using a rubber spatula until well combined. Combine the egg whites and lemon juice in the bowl of a stand mixer fitted with the whisk attachment. Beat on medium-high speed until soft peaks form. Gradually add remaining 1/3 cup of sugar and beat on high speed until stiff but not dry peaks form.
Sift flour into chocolate mixture and fold it in until well blended. Quickly fold about a one third of the egg whites into the chocolate mixture to lighten it, and then gently fold in the remaining egg whites in two parts. Pour batter into prepared pan and gently smooth the top if necessary. Bake until puffed and cracked at the surface, about 30 minutes. A toothpick or wooden skewer inserted into the center should come out with a few moist crumbs clinging to it. Cool the pan on a wire rack. The torte will sink as it cools like a soufflé should.
Remove the sides of the pan and pull off the parchment paper. Using a fine mesh sieve, sift a little powdered sugar over the top and serve with a little whipped cream or icecream if desired.