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1
Preheat the oven to 350F.
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2
Butter and flour two 8x3-inch cake pans.
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3
In a bowl, sift together the flour and baking powder.
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Set aside.
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5
To make the cake, in the bowl of a heavy-duty mixer fitted with the paddle, cream the 2 cups of butter, sugar, and scraped vanilla-bean seeds on medium speed until light and fluffy, about 3 minutes.
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6
With the mixer on low speed, add the flour mixture, alternating with the milk, beginning and ending with flour, scraping the sides of the bowl as needed.
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7
Transfer the batter to a large bowl.
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8
Switch to the whisk attachment of the mixer and use a clean bowl.
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9
Whisk the egg whites with a pinch of salt on low speed until foamy.
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Increase the speed to high and beat until stiff peaks form, 3 to 5 minutes.
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11
By hand, whisk one-third of the beaten whites into the batter to lighten the mixture.
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12
Using a large rubber spatula, fold the remaining whites into the lightened batter.
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Divide the batter between the prepared pans.
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14
Bake until golden brown and a toothpick inserted into the cakes comes out clean, 40 to 45 minutes.
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15
Remove to a rack to cool for 5 minutes.
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16
Invert the cakes onto the wire rack to cool completely.
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17
Meanwhile, for the lemon curd, prepare an ice-water bath by filling a large bowl with ice and water.
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18
To prepare the lemon curd, in a stainless steel bowl placed over a saucepan of simmering water, whisk together the egg yolks, sugar, lemon juice, and salt until blended.
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Cook, stirring constantly (to prevent the eggs from curdling), until the mixture is very thick and reaches 170F on an instant-read thermometer, about 10 minutes.
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20
Remove from the heat and immediately pour through a fine mesh strainer into a bowl to filter out any lumps or cooked egg.
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Whisk in the butter, one piece at a time, whisking until each piece of butter has melted before adding the next.
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Add the lemon zest and stir to combine.
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23
Place the bowl in the ice-water bath (or in the refrigerator), stirring occasionally, to cool.
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24
To make the frosting, switch back to the paddle attachment of the mixer and use a clean bowl.
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25
Cream the cream cheese and butter on medium speed until smooth.
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Sift over the confectioners sugar.
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Beat until light and fluffy.
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28
Add the 1/2 cup of chilled lemon curd and beat on medium speed until combined.
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Set aside.
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30
To assemble the cake, once the layers have cooled completely, halve each with a serrated knife to create 4 layers.
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31
Place one sliced layer on a cardboard cake round.
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32
Spread with about 1/2 cup of lemon curd.
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Repeat with the remaining cake layers, spreading 1/2 cup of lemon curd between each layer.
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34
Place the final cake layer bottom-side up.
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35
Using an offset spatula, cover the top and sides with frosting.
