Nutella Dobos Torte

Nutella Dobos Torte... my version Preheat the oven to 400 degrees F. Spray 2 baking pans with nonstick cooking spray, line with parchment paper, and lightly spray them again.Whip yolks and 2/3 cup powdered sugar on medium-high speed until pale and think and form a ribbon.In a clean bowl, with clean beaters, whip the egg whites on medium speed until soft peaks form. As they?re whipping, add the rest of the powdered sugar in a stream and continue whipping until you get stiff, glossy peaks.Fold 1/4 of the whipped whites into the yolks to lighten them, then fold in the rest of the whites.Stir salt into the flour, and gently fold half of the flour into the egg mixture. Fold in the rest of the flour.Divide batter evenly between the two prepared sheet pans and smooth it out with an offset spatula. Batter will be quite thin. Bake in the preheated 400 degree oven until the tops are no longer sticky when touched, about 5 -7 minutes. Let cool completely.Melt the chocolate over a double boiler and set aside to cool to lukewarm.Meanwhile beat the butter until very smooth and creamy.Beat in the cocoa powder, then the remaining powdered sugar.Next, stir in the vanilla, and finally pour in the cooled chocolate. (If the chocolate is too warm, it might melt the butter and the buttercream could become soupy. If this happens chill the loose buttercream in the fridge for half an hour until it firms up. Then beat until spreadable.)To assemble the cake (cake may be assembled up to one  day before serving)
Cut each sponge cake sheet into 6 squares. If desired, set aside a couple of squares for the caramel garnishes.Place one square on a piece of cake cardboard and coat it with a layer of buttercream. Stack another square on top, then coat with buttercream. Repeat until you have no more cake to stack.Use the remaining buttercream to frost the top and sides of the cake. Refrigerate.
Cut circles out of the remaining sponge with a cookie cutter or an inverted glass. Have them ready on a sheet pan lined with parchment paper.Boil the sugar, water and lemon juice in a pot with a light metal finish. Wash down the insides of the pot with a pastry brush dipped in water to prevent sugar crystallization.Keep cooking until the edges start to turn golden and swirl the pan to distribute the heat more evenly. Once it?s a deep amber color, remove from the heat.Very carefully spoon the caramel on the prepared sponge cake disks. Using the back of the spoon, spread the caramel to the edge of each circle. Allow the disks to cool and set up, about 15 minutes. Garnish the cake with caramel disks and hazelnuts, either crushed or whole.