The cake layers. Beat the butter with the half of the sugar until it turns white and fluffy.
Add in the egg yolks into the mixture, one by one, beating after each addition. Stir in the vanilla extract, salt, lemon zest. Set aside.
Beat egg whites until foamy. Gradually add the remaining sugar and beat until soft peaks form.
Fold the egg whites into the egg yolk mixture. Mix the sifted flour with the almond flour. Fold the flour mixture into the egg mixture.
Trace 6 9-inch circles on parchment. Spread the dough on each one of them. I've used about 1 cup of the dough on each circle.
Preheat the oven to 425 degrees F (220 C) and bake each circle for 8 minutes. Allow to cool down. Turn over and gently peel the parchment paper off. Use an 8-inch cake pan to form new flawless circles. We made the bigger circles first to make it easier to form beautiful circles later. One of these 6 circles will be used for the caramel top layer which we will cut in pieces, so you can make it slightly smaller than 8 inches (it will look better).
The chocolate buttercream. Mix egg whites and sugar in a heat-proof bowl placed over a saucepan of simmering water. Whisk continuously until sugar has dissolved and the mixture is warm to the touch (about 160 F or 71 C). Remove from the heat. Use a mixer to beat the mixture on high speed until stiff peaks form. Continue beating until the mixture is fluffy and cooled (about 6 minutes).
Add the butter gradually, beating well after the each addition, on medium-low speed. If the frosting is separated after you've added all the butter, keep beating it on medium-high speed until it comes together and is smooth (3-5 minutes more).
Beat in the chocolate and beat on low speed for about 2 minutes, to eliminate any air bubbles. Stir with rubber spatula, until smooth.
The caramel. Make sure you have all the ingredients ready because you have to act quickly. Heat the sugar in a medium saucepan over medium heat. Stir continuously with a rubber spatula. Sugar will form clumps and eventually melt as you continue to stir. Be careful not to burn.
Once the sugar is completely melted (into a thick brown liquid) immediately add all the butter. Stir until the butter is completely melted, for about 2-3 minutes. Remove the pan from heat and carefully drizzle in the heavy cream while stirring. Stir until caramel is smooth.
Butter a spatula and use it to spread the caramel over one of the cake layers which we will use on top. Butter a knife and cut layer into 8 equal pieces.
The assembling. Place the first cake layer on a plate and spread the chocolate buttercream on top. Repeat with all layers, finishing with the chocolate. I've used about ⅓ cup of buttercream on each layer. Use a pastry bag to draw with chocolate on the top layer. Place the caramel slices on top.
Frost the sides with the remaining chocolate buttercream. Use almond slices to decorate the sides of the cake.
Refrigerate overnight. Enjoy!