In a bowl, combine warm milk, melted chocolate, half of the chopped hazelnuts, and cocoa powder and mix until smooth.
Place 2 1/2 packages of cookies in a bowl and break each cookie into 4 pieces. Add the remaining chopped hazelnuts to the same bowl.
Gently pour the chocolate sauce over the crushed cookies and mix well. Make sure all the cookies are covered with the sauce.
Transfer the batter to the cake tin and press down well with a spoon to avoid air pockets.
In a separate bowl, whip the heavy cream with the melted chocolate and pour over the sponge cake layer. Place in the fridge to rest overnight.
Carefully remove the cake from the tin. Decorate with the hazelnut cream and sprinkle with chopped hazelnuts before serving. Cut out and enjoy!
