In a food processor, grind the nuts until fine. Toss in the flour. Pulse a few times to combine. Set the nuts aside.

In a large mixer bowl or in the bowl of a stand mixer, whisk the egg whites on medium speed (#6-7) until soft peaks form. With the mixer running, gradually add the granulated sugar. Increase the speed to medium-high (#7-8) and continue whipping until stiff peaks are formed.

Fold the ground nuts into the meringue in two batches.

Scoop the batter into the prepared pan and spread to an even layer.

Bake until lightly browned and firm to the touch, about 1 hour. Turn off the oven and leave the pans in the oven until completely cooled. The layer should be crisp, not spongy like a cake.

The meringues can made made 1-2 days ahead and stored at room temperature, tightly wrapped.

Toast the hazelnuts in the oven until golden brown and fragrant. If the hazelnuts have skins, fold the warm nuts in a kitchen towel and rub back and forth to remove as much skin as possible. Remove 24 nuts and set them aside for garnish.

Place the rest of the warm nuts in a food processor. Process for 4-5 minutes. At first it will look like a powder, then it will look like wet sand and eventually it will form a paste that looks like peanut butter. Stop the processor and scrap down the bowl whenever the mixture builds up on the sides. Add the confectioner's sugar to the hazelnut paste and process until combined. Stop the processor and scrape down the bowl whenever the mixture builds up on the sides. Add the hazelnut oil and process until it becomes a smooth paste. The hazelnut paste can be made ahead and stored at room temperture for a day, refrigerated for as long as a week or frozen for up to 3 months.

To prepare the reserved 24 hazelnuts for garnish, place a silicone baking mat or a sheet of parchment paper onto a half sheet pan. Have the hazelnuts set near the prepared pan. Lightly oil a dinner fork with oil or use baking spray to coat the tines of the fork.

For the caramel, sprinkle the granulated sugar into a small sauce pan. Place the pan over medium-high heat. When the edges of the sugar begin to melt, reduce the heat to medium and begin stirring with a wooden spoon to prevent spots from burning. Continue cooking the sugar until it melts completely and cooks to a golden caramel color. Immediately remove the pan from the heat.

Drop the hazelnuts into the the warm caramel. Use the greased fork to immediately lift a nut out of the caramel. Allow the excess caramel to drain back into the pan. Set the coated nut onto the parchment lined baking sheet. Continue with the remaining nuts, working quickly before the caramel in the pan begins to set. The nuts can be dipped several days ahead and stored in a covered container at room temperature.

Make the ganache according to the recipe and set aside to cool to room temperature. You can make the ganache up to 3 days ahead and refrigerate. Bring it back to room temperature and to a spreadable consistency before assembling the Marjolaine.

Make the Italian Meringue Buttercream according to the recipe. Add the hazelnut paste to the buttercream. Set aside at room temperature.

Just before you're ready to assemble the cake, make the chocolate whipped cream. The cream must be used as soon as it's made so this should not be done ahead of time.

Place the final meringue layer with the smooth side up. Smooth ice the top and sides of the cake with buttercream. Place the cake into the refrigerator for at least 2 hours until the buttercream is set firm or set into the freezer for 30 minutes. The buttercream must be quite cold to glaze the cake.

Set a cooling rack over a clean sheet pan. Use a long spatula to lift the chilled cake onto the rack.

Warm the remaining ganache in the microwave in 10 second increments until it is pourable but not very hot. Don't overheat the ganache or it will curdle. Starting from one end of the cake, drizzle the ganache over the top of the cake. Use a spatula to swipe 1x along the top of the cake and allow the ganache to flow over and completely cover the sides. Use a spatula to fill in in any bare spots. Allow the ganache to set completely before transferring the cake to a serving tray.

Using the reserved buttercream, pipe 12 rosettes along each side of the cake. You want a pair of rosettes on each slice of cake. Place a candied hazelnut on each rosette. Pipe a border of buttercream around the bottom of the cake.

Refrigerate until 1 hour before serving. The cake can be assembled up to a day in advance.