Heat the hazelnuts in a saucepan until lightly roasted. Pour in the heavy cream and bring to a light boil. Add the chopped white chocolate and stir until combined. Remove from heat and let cool to 85°F.
Roll up a piece of parchment paper and slide it inside a paper towel roll. Cover one opening with a small square piece of parchment paper and secure with a rubber band.
Pour the white chocolate hazelnut mixture into the paper towel roll until it reaches the top. Seal the open end with another square piece of parchment paper and a rubber band. Freeze for at least 2 hours.
Melt the butter, marshmallows, and cocoa powder over a double boiler. Add the Rice Krispies cereal and mix until combined.
Spread the chocolate rice krispies mixture evenly over a piece of parchment paper. Place a second piece of parchment paper on top and use a rolling pin to roll out the mixture into a flat rectangle.
Remove the frozen white chocolate hazelnut roll from the freezer. Remove the paper towel roll and parchment paper. Place the roll on top of the chocolate rice krispies.
Use the parchment paper underneath the chocolate rice krispies layer to help roll everything up into a snug log. Transfer to the refrigerator and let harden.
Spread an even layer of chocolate ice cream over a piece of parchment paper. Transfer to the freezer and freeze briefly.
Remove the ice cream layer from the freezer. Place the chocolate rice krispies roll on the lower section of the ice cream. Use the parchment paper under the ice cream layer to help roll everything up into a snug, thick log. Transfer to the freezer and freeze overnight.
Prepare the chocolate hazelnut ganache by tempering the dark chocolate and stirring in the chopped hazelnuts. Remove the Ferrero Rocher ice cream log from the freezer. Pour the ganache over it and serve.