I recently made this huge Ferrero Roche cake for a last minute order. It had three layers of 10" sponges, covered in a Nutella chocolate buttercream, with a chocolate drip and some chopped hazelnuts.
Inside the cake, there was two layers of a vanilla sponge and one chocolate layer. These were all filled with a spread of Nutella and then some chocolate buttercream. I also scattered a little bit of hazelnuts within the cake - just to add another texture alongside the usual sponge/icing texture.
The cake was then covered in the buttercream until smooth around the sides. It then had a dark chocolate drip, with the buttercream also piped onto the top. The bottom edge of the cake and also the top, was covered in chopped hazelnuts - to continue to envisage the flavours within a Ferrero Roche. The final touch on this cake, was some whole opened Ferrero Roche on the top!
I also made some super simple matching cupcakes, using the left over chocolate cake batter from the cake, and also the buttercream! These were then topped with half a Ferrero Roche and again some hazelnuts.