To make:

In a bowl, combine the warm milk, melted chocolate, half of the chopped hazelnuts, cocoa powder and mix until smooth.
Place 2 ½ packets of biscuits in a bowl and crush each biscuit into 4 parts. Add the remaining chopped hazelnuts to the same bowl.
Gently pour the chocolate sauce over the crushed biscuits and mix well. Make sure all the biscuits are covered in the sauce.
Transfer the “batter” into a springform pan and press well with a spoon to avoid air pockets.
In a separate bowl, beat the heavy whipping cream with the melted chocolate and pour over the biscuit layer. Transfer to the refrigerator to rest overnight.
Unmold the cake carefully. Decorate it with the hazelnut cream and sprinkle with chopped hazelnuts before serving. Cut and enjoy!