Preheat oven to 180°C. Grease and line a 24cm round springform tin. Using an electric mixer, beat eggs on high speed for 5 minutes or until light and fluffy. In a saucepan, bring sugar and 2 tbs water to the boil. Pour hot syrup into egg mixture and beat on low-medium speed for 6 minutes or until mixture cools and forms thin ribbons when beaters are lifted.

Sift combined flour and cocoa over egg mixture. Gently fold in, then fold in butter. Pour into prepared tin. Bake for 20-25 minutes or until a skewer inserted into the centre comes out clean. Stand in tin for 5 minutes then turn on to a wire rack to cool.

Place extra sugar and 1 1/2 tbs water in a small saucepan and boil over medium heat until sugar dissolves. Remove from heat. Allow to cool then stir in brandy.

For mousse, place all chocolate in a heatproof bowl over a saucepan of barely simmering water. Stir until melted then cool to room temperature. Meanwhile, bring 1/4 cup cream to a simmer in a saucepan over medium heat. Remove from heat. Soak gelatine in cold water for 3-4 minutes or until soft. Squeeze out excess water then add to hot cream and stir until dissolved. Cool to room temperature. Using an electric mixer, whisk remaining cream to soft peaks. Working quickly, add chocolate and gelatine mixture to cream and whisk for 1-2 seconds or until chocolate is 1/2 incorporated. Using a spatula, gently finish folding in. (If chocolate is added too slowly or over-whisked mousse will be grainy.)

To assemble cake, line base of a 24cm springform tin. Using a serrated knife, level top of sponge then place sponge in tin. Brush with brandy syrup then spoon over mousse. Refrigerate overnight or until set. Top with chocolate shavings and cocoa.