To serve:vanilla ice-cream (optional)Chocolate sponge4eggs, at room temperature110 gm(½ cup) caster sugar80 gmplain flour, sieved40 gmDutch-process cocoa25 gmbutter, meltedOrange-sherry syrup40 gmcaster sugarFinelygrated rind of ½ orange50 mldry sherryChocolate mousse150 gm eachchocolate (53% cocoa solids) and dark chocolate (70% cocoa solids), coarsely chopped590 mlthickened cream, at room temperature ¾titanium-strength gelatine leaf, soaked in cold water for 5 minutes80 gmglacé orange, finely chopped, plus extra to serve40 gmroast hazelnuts, coarsely chopped, plus extra, sliced, to serveChocolate ganache85 mlpouring cream40 gm eachchocolate (53% cocoa solids) and dark chocolate (70% cocoa solids), finely chopped10 gmsoftened butter
For chocolate sponge, preheat oven to 180C. Whisk eggs on medium-high speed in an electric mixer until light and fluffy (6-8 minutes). Meanwhile, stir sugar and 2 tbsp water in a small saucepan over high heat to dissolve, then bring to the boil. Pour hot syrup into egg mixture and whisk on medium speed until mixture cools and forms thin ribbons (6 minutes). Sieve over flour and cocoa, fold in, then fold in butter. Pour into a greased 22cm springform tin lined with baking paper and bake until a skewer inserted in the centre withdraws clean (20-25 minutes). Stand in tin for 5 minutes, turn onto a wire rack to cool completely. Halve cake horizontally with a serrated cake knife and set aside, cut-side up.
Meanwhile, for orange-sherry syrup, bring sherry, sugar and orange rind to the simmer in a small saucepan over medium heat. Cool, brush generously over sponge, place one sponge half in a baking paper-lined 22cm springform pan and set aside.
For chocolate mousse, melt chocolates in a heatproof bowl over a saucepan of simmering water, cool to room temperature. Meanwhile, simmer 40ml cream in a small saucepan over medium heat, remove from heat, squeeze excess water from gelatine and add to cream, stirring to dissolve, then cool to room temperature. Whisk remaining cream to soft peaks in an electric mixer, then, whisking continuously, add chocolate mixture and gelatine mixture and whisk until chocolate is half-incorporated (do not over-whisk). Fold in with a spatula to fully incorporate. Fold through half the glacé orange and hazelnuts, pour over sponge in prepared pan, smooth top and sandwich with remaining sponge. Refrigerate until set (4-6 hours or overnight).
Meanwhile, for chocolate ganache, bring cream just to the boil in a small saucepan over high heat. Place chocolate in a bowl, add cream and butter, stand until chocolate melts (2-3 minutes), then stir until smooth and glossy. Set aside, stirring occasionally, until starting to thicken (10-20 minutes).
Remove cake from pan, place on a wire rack over a tray, spread ganache over cake with palette knife. Refrigerate cake until semi-set (5-10 minutes). Serve topped with remaining orange and hazelnuts, with ice-cream and extra orange and hazelnuts to the side.
To celebrate our deputy editor's birthday, GT ordered one of
Sydney pâtissière Lorraine Godsmark's creations: its delicious
layers inspired the recipe for this rich dessert cake. You'll need
to begin this recipe a day ahead.