• 1 1/2 sticks (170 g) unsalted butter, plus extra for greasing
• flour, for dusting
• 6 ounces (170 g) bittersweet chocolate
• 1 cup plus 2 tablespoons (220 g) sugar
• zest of one large orange
• 4 eggs plus 2 egg yolks
• 1/2 cup (55 g) unsweetened cocoa powder
• 10x confectioners’ sugar, for dusting
• candied orange peel and vanilla ice cream, to serve

Preheat the oven to 375°F (190°C). Butter and flour a 10-inch (25-cm) round cake pan. Line the bottom of the pan with parchment paper, then butter and flour the parchment paper. Gently melt the chocolate over a double boiler. Stir the butter into the chocolate to melt, and stir until smooth. Remove from the double boiler and whisk the sugar and orange zest into the chocolate mixture. Add the eggs and egg yolks and whisk well. Sift the cocoa powder over the chocolate mixture and whisk the batter until totally smooth. Pour the batter into the pan and bake for approximately 35 to 40 minutes, or until the top has formed a good crust. Cool the cake in the pan on a rack for 10 minutes. Invert the cake onto a serving platter. Dust with confectioners’ sugar and serve with candied orange peel and vanilla ice cream.