Let’s build this luxurious cake step-by-step:

1. Prepare Pans and Preheat Oven: Preheat oven to 350°F (175°C). Line two 8-inch round cake pans with parchment paper and spray the sides with non-stick spray.

2. Melt Chocolate & Nutella: Melt the bittersweet chocolate chips in a microwave (short bursts, stirring often) or over a double boiler. While the chocolate is still hot, add the Nutella and whisk until completely smooth. Set aside to cool slightly.

3. Prepare Hazelnut Flour Mixture: If using whole hazelnuts, place them in a food processor with the all-purpose flour, cocoa powder, baking powder, salt, and confectioner’s sugar. Pulse until a fine flour forms. If using pre-ground hazelnut flour, simply whisk these dry ingredients together in a bowl. Set aside.

4. Make Cake Batter Base: In the bowl of a stand mixer (paddle attachment), beat the softened butter and granulated sugar on high speed until light and fluffy. Add the Frangelico and egg yolks; mix until well combined.

5. Combine Mixtures: Gently fold the slightly cooled chocolate/Nutella mixture into the butter/yolk mixture. Then, gently fold in the hazelnut flour mixture until just combined. Do not overmix.

6. Whip and Fold Egg Whites: Transfer the chocolate batter into a separate large bowl. Thoroughly clean and dry the mixer bowl and whisk attachment. Place the egg whites into the clean mixer bowl and whisk on high speed until stiff peaks form. Gently fold the whipped egg whites into the prepared chocolate cake batter in thirds, being careful not to deflate the egg whites too much. Fold gently until a uniform batter forms.

7. Bake Cake Layers: Pour the batter evenly into the prepared cake pans. Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 35-40 minutes.

8. Cool Cake Layers: Remove cakes from pans and let cool completely on wire racks. The recipe notes these layers will be fragile; handle carefully.

9. Split Cake Layers: Once completely cooled, carefully split each cake layer in half horizontally using a long serrated knife, forming 4 thin layers total.

10. Make Nutella Frosting: Place the softened butter and Nutella into a clean mixer bowl (paddle attachment). Whisk on medium-high speed until light and fluffy, about 5 to 6 minutes. Gradually add the confectioner’s sugar, mixing on low speed initially, then increasing speed until the frosting is thick and fluffy, mixing for another 3 to 4 minutes. Add the pinch of salt, if desired.

11. Assemble the Cake:

• Place the bottom cake layer onto your serving plate or cake board.
• Lightly brush the layer with Frangelico (or your chosen soak).
• Spread a layer of Nutella frosting evenly over the soaked cake.
• Sprinkle a generous layer of crushed wafer/waffle cookies over the frosting.
• Place the next cake layer on top. Repeat the soaking, frosting, and crushed cookie process for the next two layers.
• Place the final (fourth) cake layer on top. Lightly brush this layer with the soak as well.

12. Frost and Garnish:

• Apply a thin crumb coat of frosting over the entire cake (top and sides) and chill for 30 minutes.
• Apply the remaining Nutella frosting smoothly over the top and sides of the cake.
• Garnish the top decoratively with whole Ferrero Rocher candies and whole or chopped hazelnuts. You can also press more crushed cookies around the base.

13. Chill and Serve:

• Keep the Ferrero Rocher cake refrigerated.
• When ready to serve, remove the cake from the refrigerator about 1 hour before serving to allow the buttercream to soften slightly for the best texture and easier slicing.

This assembly creates the full Ferrero Rocher experience!