Method

• 1.
  Preheat oven to 180°C. Grease the base and sides of a 23cm springform cake tin and line with baking paper.
• 2.
  To make the cake, in a stand mixer fitted with the whisk attachment, whisk eggs and sugar for 7 minutes or until pale and tripled in size. Sieve flour, cocoa, baking powder and ¼ tsp fine sea salt into a bowl. Gently fold flour mixture into egg mixture in 2 batches. Fold in butter. Pour into prepared tin and bake for 35 minutes or until a skewer inserted in the centre comes out clean. Cool cake completely in tin, then remove and, using a large serrated knife, cut horizontally into thirds. Grease base and side of cleaned cake tin and line with baking paper. Place top third of cake in the base of the pan.

• 3.
  For the pâte à bombe, combine sugar, glucose and 2 tbs water in a small saucepan. Bring to the boil, stirring continuously, until sugar dissolves, then simmer for 5 minutes or until 120°C on a sugar thermometer. In the cleaned stand mixer fitted with the whisk attachment, whisk yolks until pale. With the motor running, add sugar syrup in a steady stream and whisk for 10 minutes or until cooled. Divide evenly between 2 bowls.
• 4.
  For milk chocolate mousse, fill a small saucepan to a third full with water and bring to a very gentle simmer. Place chocolate and butter in a small heatproof bowl, place over pan (don’t let the bowl touch the water) and melt without stirring. Set aside to cool. Whisk cream to medium peaks. Fold 1 batch pâte à bombe mixture into chocolate mixture, then, in 2 batches, fold in whipped cream. Chill for 2 hours to firm slightly.
• 5.
  For dark chocolate mousse, fill a small saucepan to a third full with water and bring to a very gentle simmer. Place chocolate and butter in a small heatproof bowl, place over pan (don’t let the bowl touch the water) and melt without stirring. Set aside to cool. Whisk cream to medium peaks. Fold orange zest, orange oil and remaining pâte à bombe into chocolate mixture, then, in 2 batches, fold in whipped cream. Spread mousse over cake, leaving a 5mm border. Chill for 1 hour or until set.
• 6.
  Top dark chocolate mousse with middle third of cake. Spread milk chocolate mousse over cake, leaving a 5mm border. Chill for 2 hours or until firm, then top with remaining cake. Chill for a further 2 hours or overnight to set. Transfer to a large serving plate.
• 7.
  For chocolate glaze, soak gelatine in cold water for 5 minutes to soften. In a bowl, whisk cocoa and ¼ cup (60ml) water to form a smooth paste. Combine cream and sugar in a saucepan over medium-high heat and stir constantly until sugar dissolves. Squeeze excess water from gelatine and stir gelatine and cocoa mixture into cream mixture until dissolved. Pour glaze over top of cake only, allowing some to drip over the edge.