Adapted from Maida Heatter’s Great Book of Desserts and Joe Pastry. I made this with chocolate Swiss meringue buttercream instead of the traditional chocolate buttercream because I prefer the taste but just be aware that although SMBC tastes best at room temperature it will also soften to the point that your little hazelnut towers might lean.
7 large eggs, separated
3 large egg yolks
1 pound (3 1/2 cups or 455 grams) confectioners’ sugar
3/4 cup (94 grams or 3 1/3 ounces) all-purpose flour
1 tablespoon lemon juice
1/8 teaspoon table salt
Chocolate Swiss Meringue Buttercream Frosting and filling:
4 oz egg whites (I used liquid All Whites)
6 oz granulated sugar
12 oz unsalted butter
1 Tablespoon vanilla extract
5 oz dark chocolate, tempered and cooled slightly but still pourable
3/4 cup granulated sugar
2 Tablespoons water
12 peeled hazelnuts
piping bag fitted with flower tip
9″cake board or cake plate
Cut out eight 12″x 17″ pieces of parchment paper and trace a 9″ circle on each one (you can use the bottom of a cake pan or a cake board for this). Spray each piece liberally with your choice of cake pan spray and dust with confectioner’s sugar. Lay out the pieces on your counter. Also, have ready several cooling racks lightly sprayed with cake pan spray.
For the cake: Preheat oven to 450°F and place a rack in the center of your oven. In the bowl of an electric mixer, beat the 10 egg yolks for a few minutes at high speed, until pale and lemon-colored. Reduce speed and gradually add sugar, then increase the speed and beat the yolks and sugar until thick and glossy. Scrape bowl occasionally with rubber spatula. Reduce speed again and gradually add flour and salt; increase speed and beat for 5 minutes more, then stir in lemon juice. Scrape bowl again with a rubber spatula. In a separate bowl with a clean whisk, beat the 7 egg whites until they hold stiff peaks. Stir a few heaping spoonfuls of the whites into the yolk mixture to loosen it. Then fold in the rest of the whites in three additions.
Spread about 1/2-3/4 cup of batter onto each piece of parchment paper and spread it to the edges of circles with an offset spatula. Spread batter to about 1/4-inch thickness in each circle. Be careful not to leave any holes in the batter. You will slide each parchment piece onto the cookie sheet right before baking.
Bake each layer for 5-7 minutes, or until golden with some dark brown spots. It took me exactly 7 1/2 minutes of baking for each layer to ensure that the parchment paper would easily peel off . When layer is baked, remove it from the oven and immediately flip it out onto a cooling rack and carefully peel off the parchment paper.
Once cooled you can again use your 9″ cake pan or board to trim the layers with a pizza wheel.
For the chocolate Swiss meringue buttercream: In a bowl of an electric mixer, lightly whisk egg whites and sugar together over simmering water until the egg-sugar mixture is very warm to the touch and the sugar crystals are completely dissolved (or a candy thermometer reads 140°F (60°C)). Place the egg-sugar syrup into mixer and whip on high with the wisk attachment until the bowl has cooled to almost room temp (approx. 15 minutes). Meanwhile cut up butter into two-inch pieces. Turn mixer down to “stir” or the low setting and begin adding the butter pieces a few at a time over a minute or two until all the butter is added. Turn mixer up to medium-low speed and incorporate all the butter for a few minutes. Take off wisk attachment, scrape bowl, and put on paddle attachment. Continue to mix at medium high speed for another five minutes or until mixture emulsifies into a soft buttercream. Add vanilla extract and cooled chocolate and mix for another few minutes until incorporated.
Assemble the cake: Place first cake layer on a 9″ cake board and spread chocolate on top and to edges with an offset spatula. The filling must be spread fairly thinly to have enough for all layers and the outsides of the cake. Repeat for 6 more layers and reserve the last cake layer for your caramel. Then crumb coat the entire cake, reserving about 1/4 cup buttercream for the hazelnut towers. You could also refrigerate the cake for about 30 minutes then add a final coat of frosting but I did not. Use a flower tip to pipe 12 “towers” for the hazelnuts — think of a clock when piping your towers. Add a hazelnut to the top of each tower and chill for about 30 minutes or until firm.
Caramel topping: Lightly grease a sheet of parchment paper. Place last cake layer on this sheet. Lightly grease a large chef’s knife and a pizza cutter and set aside. Combine the sugar and water in a small, heavy saucepan and swirl it until the sugar melts and begins to turn a pale amber color. Quickly and carefully, pour this (you’ll have a bit of extra) over the prepared cake layer and spread it evenly with an offset spatula right over the outer edges. Wait about a minute then use your pizza wheel to trim the outside edge. Using the prepared knife, quickly cut into 12 pieces by first cutting into half then quarters, then eighths, then sixteenths (again think of a clock). Leave in place, then cool completely. Once fully cooled, cut edges of shapes again, to ensure that you can remove them cleanly. Arrange caramel pieces or wedges over cake, propping them up decoratively with the hazelnuts.
Chill cake until needed for a few hours before serving. Cake can be stored in the refrigerator for 3-4 days.