Preheat the oven to 350°F and gather all the ingredients.
In the bowl of a stand mixer, whisk the eggs with the sugar until the mixture doubles in volume.
In a separate bowl, sift the flour and cacao powder.
In thirds, use a spatula to fold the flour mixture into the egg mixture, being extra careful not to over-mix the dough.
Stir in 3/4 cups of the crushed hazelnuts. Spread the cake batter onto a baking sheet lined with parchment paper (10in. X 15in. is the ideal size). Bake the cake for 12 minutes.
Remove the cake from the oven. Lift the cake up by the edges of the parchment paper and place it on top of a kitchen towel. Starting with either shorter end of the cake, roll it up into a log. Allow the cake to cool to room temperature.
Making the Cake Cream
In the bowl of a stand mixer, beat the butter, dulce de leche, and Nutella together until the ingredients are well-combined. Set the cake cream aside.
Combine the heavy whipping cream with the sweetened condensed milk. Unroll the cake and spread the sweet cream mixture over the cake and allow it to soak for a few minutes.
Spread 3/4 of the cake cream on to the inside of the roll. At one of the edges, assemble the Ferrero Rocher candies side by side.
Spread 3/4 of a cup of the crushed hazelnuts over the cake cream. Roll the cake back up and frost the outside of the cake with the remaining cake cream. Sprinkle the rest of the hazelnuts on top.
Melt the chocolate in the microwave, stirring it every 10 seconds until silky and fully melted. Place the chocolate in a piping bag and drizzle the cake with it. Slice the wrapped candies in half and decorate the top of the cake with them.
Let the cake set in the refrigerator overnight. Serve cold or at room temperature and enjoy!