Preparation

• 1 Preheat an oven to 350°F. Butter and flour an 8-inch springform pan with 2-inch sides.
• 2 In a bowl, sift together the flour, cocoa powder and espresso powder. Set aside.
• 3 Place the chocolate in a heatproof bowl and set over but not touching barely simmering water in a saucepan. Melt the chocolate, stirring occasionally. Remove the bowl from the heat and stir in the butter, a little at a time, until blended. Let cool slightly.
• 4 In a large bowl, combine the egg yolks and superfine sugar. Using an electric mixer set on medium speed, beat until creamy, 3 to 4 minutes. Beat in the chocolate mixture until blended. Fold in the flour mixture and then the vanilla.
• 5 In another large bowl, beat the egg whites until soft peaks form. Stir one-fourth of the whites into the batter, then fold in the remaining whites just until incorporated.
• 6 Pour the batter into the prepared pan and level the top. Bake until the top is risen and crusty and a toothpick inserted into the center comes out almost clean, 30 to 35 minutes. The center should be soft and moist. Transfer the pan to a wire rack and let cool for 10 to 15 minutes. The top will fall a bit. Remove the pan sides, loosen the cake's edges with a knife, and slide the warm cake onto a serving plate.
• 7 To make the whipped cream topping, in a bowl, whisk together the cream and sour cream until slightly thickened. Whisk in the confectioners' sugar, orange zest and vanilla until soft peaks form.
• 8 Dust the warm cake with confectioners' sugar. Cut into slices and top with whipped cream.