No bake chocolate hazelnut slice

Grease a 30cm x 8cm rectangular loose-bottomed fluted tart tin with cooking oil spray. Line base with baking paper.

Put biscuits into a large zip-lock bag and crush with a rolling pin until a fine crumb forms. Transfer to a large bowl and stir in cocoa and butter. Press into the bottom of prepared tin and refrigerate until firm.

Put dark chocolate into a large heatproof bowl of a saucepan of simmering water and stir until half-melted. Set aside off the heat. 

Pour 200ml of cream into a small saucepan and bring to a boil over medium heat. Add to dark chocolate and whisk until smooth. Sit bowl in a large bowl of iced water, ensuring no water gets into the chocolate mixture and beat until thick and aerated. Fold in ¾ cup of the hazelnut, then spoon on biscuit base and smooth surface. Refrigerate until firm.

Heat remaining cream in a small saucepan. Once boiling, remove from heat and whisk in milk chocolate  until smooth. Refrigerate for 10 minutes or until slightly thickened and spreadable. Remove slice from tin. Spread over slice and scatter with the remaining hazelnuts. Refrigerate for 5 minutes until set, then slice into pieces.