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["Preheat the oven to 350u00b0F. Draw two 6 inch circles onto a piece of parchment paper using a thick pen or marker. Turn the paper over onto a baking sheet, so you can still see the marks but the ink won't touch the food. On two more pieces of parchment, draw lines spaced 4 inches apart across the short side of the parchment paper (see pictures inside the article for a visual cue). Turn the papers over onto their own baking sheets.", "Make the sponge batter: sift the flour and salt onto a piece of parchment paper. In the bowl of an electric mixer fitted with the whip attachment, whip the egg yolks, orange zest, vanilla extract and HALF of the sugar on medium high speed until the mixture is pale and thick, 2-3 minutes. Transfer to a large bowl and set aside. Wash and dry the mixer bowl and whip attachment.", "In the bowl of the mixer fitted with the clean whip attachment, whip the egg whites and remaining sugar on medium high speed until they reach medium peaks, 3-4 minutes. Do not overwhip - the whites should be shiny and smooth, not clumpy or stiff.", "Gently fold the flour mixture into the egg yolk mixture with a silicone spatula. Mix just until combined - do not overmix.", "Add 1/4 of the whites to the yolk mixture and mix to combine. You can mix slightly more vigorously at this point to ""temper"" the batter with the egg whites (this makes it easier to combine the remaining whites and helps maintain better volume).", "Gently fold in the remaining whites in 2-3 additions, folding just until they are combined in the batter -do not overmix, it can make the batter lose volume, leading to deflated cakes!", "Transfer some of the batter to a disposable piping bag fitted with a 1/2 inch round tip. Begin by piping the cake layers (you've prepared guides for yourself by tracing two 6 inch circles onto a piece of parchment). Pipe the batter into a spiral, starting from the center of the traced circle. Repeat with the second circle.", "Transfer the tray to the oven and bake until the cakes spring back gently when touched in the center, 17-20 minutes. They won't brown much.", "Transfer the remaining batter to the pastry bag (same one you used before!) and have ready your other two baking sheets prepared with 4 inch guides. Pipe the ladyfingers by starting at one line and piping down to the other in a straight line. Leave at least 1 inch between each and stagger them on the baking sheet to prevent the batter from running together (see photos in article for visual cue!).", "Transfer the pans to the oven and bake until the ladyfingers spring back gently when touched, 12-15 minutes. They won't brown much.", "Cool both the cakes and ladyfingers completely. Line a baking sheet with parchment and place a 9 inch springform pan on top. If desired, line the side of the pan with parchment as well. When the cakes are cool, prepare the mousse. Remember, it will begin to set up quickly so have everything ready to go before you make the mousse.", "Ladle a small amount of mousse into the base of the pan - just enough to evenly cover the whole base. Arrange the ladyfingers around the sides of the pan, with the rounded side facing out, and the flat side (the side that touched the pan during baking) facing inward. Use the thin layer of mousse at the bottom of the pan to help ""anchor"" the ladyfingers to keep them in place. Place them snugly side by side - you want to avoid gaps between them.", "Place the first cake layer into the pan, placing it on top of the mousse on the base of the pan and pressing down slightly. Ladle half of the remaining mousse on top of the cake layer.", "Place another cake layer on top of this mousse layer, and press it down slightly so it settles into the mousse. Then, ladle the remaining mousse on top. Don't worry too much how the surface looks, as long as it's an even layer.", "Place the cake into the freezer (you an also put it in the refrigerator, but freezing at this point makes unmolding easier and faster). Chill until totally set.", "When the cake is set, unmold it. Release the outer ring of the springform pan and peel away the paper from the outside edge. Run an offset spatula all around the base of the cake to help release it, then transfer it to a platter or cake stand.", "Decorate the surface with citrus segments. If you fully froze the cake, let it thaw before serving. Otherwise, store the cake in the refrigerator until ready to serve."]
