Lemon Chiffon Layer Cake

Directions

1. Heat the oven to 325°F. Grease two 9-inch cake pans, place a parchment round in the base, then grease and flour the edges of the pan.
2. Make the cake: Sift together the cake flour, making powder, and salt into a medium bowl. In a container with a pour spout (such as a 2-cup liquid measure), whisk together the oil, milk, vanilla, and lemon extract.
3. In the bowl of a stand mixer fitted with the whisk attachment (or in a large bowl, using a hand mixer), whip the egg yolks on medium speed until slightly pale, 1 to 2 minutes. Gradually add 1 cup (198 grams) of the granulated sugar and whip the mixture on medium-high speed until it becomes pale and thick and has quadrupled in volume, 4 to 5 minutes.
4. Reduce speed to low and add the lemon zest, then whip for 1 minute more to help stabilize the foam. Gradually add the milk mixture to the mixer in a slow, steady, stream, mixing on low speed to combine.
5. Sprinkle about 1/4 of the flour mixture into the mixer bowl and mix on low speed until just incorporated. Add the remaining flour in 3 more additions, mixing just until incorporated.
6. In a clean, dry electric mixer bowl, combine the egg whites and cream of tartar. Mix on medium speed until foamy, 1 to 2 minutes. Turn up the speed to medium high, add the sugar, and whip the egg whites to medium peaks, 4 to 5 minutes.
7. Fold about 1/4 of the egg whites into the batter, mixing thoroughly (this first addition helps to temper the batter, making it easier to incorporate the rest of the whites without deflating them). Add the remaining whites in 2 to 3 more additions, folding just until incorporated.
8. Divide the batter between the prepared pans and gently spread into an even layer. Transfer to the oven and bake until the cakes spring back slightly in the center when touched, 50 to 55 minutes. Cool the cakes in the pans for 10 minutes, then invert onto a rack to cool completely.
9. Make the lemon syrup: Combine the lemon juice and sugar in a small saucepan and bring to a boil over medium heat, stirring to help dissolve the sugar. Set aside to cool to room temperature.
10. Make the buttercream: Place the egg whites and cream of tartar in the bowl of an electric mixer fitted with the whisk attachment. In a medium saucepan, combine the sugar and water and bring to a boil over medium heat. Stir until the mixture begins to bubble, but as soon as bubbles appear, stop stirring. If necessary, dip a pastry brush in cool water to brush away granules of sugar that appear on the side of the pot.
11. Cook the sugar mixture to 235°F. Begin whipping the egg whites on medium-high speed. When the sugar mixture reaches 240°F, remove the pot from the heat and gradually add the hot sugar syrup to the mixer in a slow, steady stream. Continue whipping until the meringue has reached full volume and the bowl is no longer warm to the touch, 5 to 6 minutes.
12. With the mixer running on medium speed, gradually add the butter a few tablespoons at a time, mixing to fully combine before adding more. When all the butter is added, mix in 1 cup (240 grams) lemon curd and mix well to combine. Transfer about 1/4 of the buttercream to a pastry bag and cut 1/2-inch opening from the end.
13. Assemble the cake: Use a serrated knife to remove the domed top of the cakes, if desired, and then cut each cake into 2 layers—you should have 4 layers total.
14. Place one layer on a cake turntable, platter, or cake stand. Pipe a ring of frosting around the outside edge of the cake. Use an ice cream scoop (about 1/4-cup in size) to scoop 3 scoops of the remaining lemon curd into the center and spread into an even layer. Place another layer of cake on top, and repeat this process. Continue until you’ve used all the filling and layers.
15. Apply a thin all over “crumb coat” of the frosting, and chill the cake for 10 to 15 minutes. Frost the cake with the remaining frosting. Finish with lemon zest.