This recipe is from Lomelino's Cakes, and combines a delicious lemon curd filling inside of an airy cake made with lemon zest + juice. It's coated with a layer of lemon-y buttercream, for a perfectly sweet-yet-tart cake that's perfect for any lover of lemon.
Separate the eggs and whites into separate bowls so you have 4 whites and 3 yolks (you can save the extra yolk for something else). Allow them to come to room temperature.
Preheat the oven to 325 degrees Fahrenheit. In a medium bowl, sift together the flour, cornstarch, 1/2 cup sugar, baking powder, and salt. In a separate bowl, whisk together the vegetable oil, egg yolks, lemon juice water, lemon peel, and vanilla sugar. Sift the dry ingredients over the bowl with the wet ingredients and stir until the batter just comes together. Set aside.
Remove the pans from the oven and immediately turn them upside down onto a wire rack to cool to prevent the layers from collapsing at the center.
Allow the cake layers to rest upside down in the pan until they're completely cooled. Take a butter knife and gently loosen the cake around the edges of the pan. Hold each pan and shake gently to unmold the layers from the pan. Set the unmolded layers aside on the wire rack while you prepare the curd and lemon cream.
Mix the sugar, egg, lemon peel, and lemon juice into the top of a double boiler with simmering water in the bottom layer. Use a hand whisk to beat the mixture constantly so the curd doesn't harden and get chunky, you want to keep it nice and smooth. It should be the same consistency as hollandaise sauce when it is done.
Beat the cream and sugar together until soft and fluffy. Fold in the lemon curd.
To assemble the cake, slice each layer in half horizontally so you have 4 thin layers for the cake. Place the first layer on the serving dish and spread an even layer of the lemon curd over the top of it. Repeat until you've covered 3 layers with the lemon curd. Place the last cake layer on top, cut side down. Cover the entire cake with an even layer of the lemon cream.