Bittersweet Chocolate Cake

INGREDIENTS

• 3 Tbs. cake flour
• 1 Tbs. Dutch process cocoa powder
• 2 tsp. instant espresso powder
• 5 oz. bittersweet chocolate, chopped into chunks
• 6 Tbs. (3/4 stick) unsalted butter, cut into small
• cubes, at room temperature
• 4 eggs, separated
• 1/2 cup superfine sugar
• 1 tsp. vanilla extract
• 1 cup heavy cream
• 2 Tbs. sour cream
• 2 Tbs. confectioners’ sugar
• 1 Tbs. finely grated orange zest
• Confectioners’ sugar for dusting