serves eight to ten
soft butter or shortening (to grease pan) greaseproof or silicone paper (parchment is OK)
13 ounces bittersweet chocolate, broken into small pieces
2 tablespoons unsalted butter, softened
2 tablespoons castor sugar
12 egg yolks
12 egg whites
cocoa or grated chocolate and whipped cream (for garnish)
Preheat oven to 300 degrees. Prepare an 8-to-10-inch springform pan by first greasing, then lining with baking paper. (The parchment should be on the bottom only in the form of a round disk that covers the base. The butter helps to hold it in place.)
Place the chocolate pieces into a double boiler and melt the chocolate. Beat the butter, sugar, and egg yolks with an electric mixer for a few minutes, or until pale in color. Add this mixture to the just-melted chocolate; mix gently and set aside.
Beat the egg whites until stiff peaks form. Add about a quarter of the beaten egg whites into the melted chocolate base. Gently fold to combine, and then continue to fold in the remaining whites. Pour two-thirds of this mixture into the cake pan. (Put the remaining mixture in the fridge, covered with plastic film.) Bake the cake for 40 to 50 minutes; when the cake feels firm and springy, remove from the oven. Slide a knife around the outside, then remove the springform tin, turning it out upside down onto a serving platter while it’s still hot. Allow the chocolate cake to cool for a least one hour. The center should fall in. Fill this space with the cold remaining mixture, dust with cocoa or chocolate, and serve with whipped cream.