Method

• 1.
  Preheat oven to 160°C. Grease the base and side of a 24cm springform cake pan and line with baking paper. Place chocolate and butter in a bowl set over a saucepan of gently simmering water and stir until melted and smooth (mixture may look a little split but will come back together). Set aside to cool. Whisk eggs and sugar vigorously together in a bowl until well combined and sugar has partially dissolved. Whisk in hazelnut meal, flour and cooled chocolate mixture. Pour into prepared pan and place on a baking tray. Bake for 50 minutes or until edges are set but centre is still a little bit wobbly. Cool to room temperature, then chill until cold.
• 2.
  For the white chocolate mousse place chocolate in a heatproof bowl set over a saucepan of simmering water (don’t let the bowl touch the water) and stir until melted and smooth. Cool slightly.
• 3.
  Soak gelatine in cold water for 5 minutes to soften. Place 150ml cream in a small saucepan over low heat and bring to a simmer. Squeeze excess water from gelatine and stir into cream until melted and combined. Set aside to cool, then beat into chocolate mixture.
• 4.
  Place remaining 300ml cream in a bowl and whisk to stiff peaks. Set aside. Beat one third of the whipped cream into the chocolate mixture, then fold in remaining cream in 2 batches. Pour over the cake base and chill overnight until set. Scatter over hazelnuts to serve.