Mix the crushed biscuits with the melted butter and milk until combined. Press firmly into a lined 20×20 cm pan. Chill while preparing the filling.
Beat the no-cook chocolate pudding powder with the cold milk until thickened.
Add the heavy cream and beat until smooth and mousse-like.
Spread the filling evenly over the base and refrigerate for 1 hour.
Heat the heavy cream until steaming. Pour it over the chopped chocolate, let it sit for 1 minute, then stir until smooth.
Pour the chocolate topping over the chilled filling.
Decorate with Ferrero Rocher and chill until fully set, at least 2 more hours or overnight for best results.
Slice into squares and serve.