Preheat the oven to 325 degrees F on convection or 350 degrees F in a regular oven.
In a large bowl, whisk together the hazelnut and all purpose flour, breaking up any lumps. Set aside.
In the mixing bowl of a 20-quart standing mixer set on high speed, whip together the whole eggs and 2 pounds of sugar until tripled in volume, pale yellow and forming thick ribbons, warming the bowl of the mixer with a propane torch to increase the volume of the eggs. Set aside.
In another mixing bowl of a 20-quart standing mixer set on high speed, whip the egg whites and remaining 1 3/4 pounds sugar until thick, glossy, and firm peaks form. Fold the flour mixture into the whole egg and sugar mixture, and then fold in the egg whites.
Divide the batter equally onto 6 (18-by-26-inch) parchment lined baking sheets. Bake until the corners brown and the batter doesn't adhere to your fingers when you touch the cake, 5 to 7 minutes. Remove from the oven and cool completely.
To assemble the cake: Place a layer of the hazelnut cake on a prepared cake board or inverted sheet pan. Brush with about one-sixth of the simple syrup and spread a generous layer of the buttercream over top. Place another layer of the cake on top and soak with the simple syrup. Spread a layer of buttercream and then a layer of ganache. Place the next layer of cake and repeat the previous steps until you have used all 6 layers of hazelnut sponge cake, ending with a layer of buttercream on the top. Chill the cake completely to set. When chilled, trim the sides, and frost with a final layer of buttercream, reserving some buttercream for garnish. Return to the refrigerator again to set the top. Spread the remaining ganache over the top to make a smooth finished coat. Trim any excess ganache from the sides of the cake. Press the toasted and chopped hazelnuts onto the sides of the cake. Decorate the cake with buttercream piped from a star tip filled pastry bag, and decorate with the gilded hazelnuts.
Combine all of the ingredients and bring to a boil. Cook until the sugar is dissolved and the alcohol has evaporated. Cool completely.
Pour sugar and just enough water to moisten it in a large heavy bottomed pot. Bring sugar to a boil, stirring constantly. Brush down any sugar crystals that form on the side of the pot with pastry brush dipped in water. Once the sugar has come to a boil, stop stirring and cook the sugar to the soft ball stage or 240 degrees F on a candy thermometer. When the sugar reaches 240 degrees F, reduce the heat to low and whip the egg whites on high speed in a 20-quart standing mixer to firm peaks. While the mixer is on high, carefully pour the melted sugar into the whipped egg whites, being careful not to burn yourself on the molten sugar. Once the sugar is combined with the egg whites, reduce the mixer speed to medium, and continue to whip the egg whites and sugar until completely cool, approximately 30 minutes. When the egg white meringue is cool, turn the mixer back up to high, and gradually add the cubed butter. The butter may separate and become watery, but continue to whip on high until the water is re-incorporated. It is very important that the egg white meringue is completely cool so as not to melt the butter. When all the butter has been added, continue to beat until the buttercream is smooth and creamy. Reduce the mixer speed to low and add the coffee and vanilla extracts.
Place chocolate pieces in a large bowl. Bring the heavy cream and Frangelico to a boil and pour over the chocolate. Let stand 3 to 5 minutes and then whisk together until smooth and all of the chocolate is melted. Allow the ganache to cool to room temperature so it reaches a spreadable consistency.
Lightly spray the hazelnuts with nonstick cooking spray and wipe off any excess. Place a single nut on the gold leaf and gently brush the gold onto the nut. Set aside to garnish the finished cake.
Gold leaf is edible and available at specialty spice and pastry supply stores.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.