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1
Preheat the oven to 350F.
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2
Butter 2 8 x 2-inch round cake pans, and line with parchment paper.
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3
Butter the parchment, and dust the bottoms and sides with flour, tapping out excess; set aside.
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4
Into a medium bowl, sift together the flour, baking powder, and salt twice; set aside.
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5
In a mixing bowl, using the paddle attachment, cream the butter on low speed until soft.
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6
Increase speed to medium; beat until pale and fluffy.
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7
Gradually add 1 1/2 cups sugar; beat until fluffy, about 3 minutes.
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8
Beat in the vanilla, poppy seeds, and lemon zest.
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9
With the mixer on low speed, add the flour mixture in 2 batches, alternating with the milk; beat until thoroughly combined after each addition.
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10
Scrape the sides of the bowl; beat 10 seconds more.
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11
Set aside.
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12
In another mixing bowl, whisk the egg whites and cream of tartar on low speed until foamy.
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13
Increase speed to medium-high; gradually add the remaining 1/4 cup sugar until the peaks are just stiff.
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14
Gently fold in the whites; do not overmix.
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15
Divide the batter between the prepared pans; bake until golden and a cake tester inserted in the centers comes out clean, about 40 minutes.
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16
Transfer to a wire rack to cool completely.
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17
To remove the cakes, invert onto plates; peel off the parchment paper, and reinvert so the top side is up.
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18
Make the filling: In a small bowl, whip the heavy cream to soft peaks.
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19
Fold in the lemon curd; cover with plastic, and refrigerate until chilled and firm, at least 2 hours.
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20
Assemble the cake: Using a serrated knife, trim the tops of both cakes to make level, if desired.
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21
Slice each in half horizontally to make a total of 4 layers.
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22
Brush away crumbs from the tops of the layers.
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23
Place one of the bottom layers on a serving platter; spread with 1 cup lemon filling.
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24
Top with another cake layer; spread with 1 cup filling.
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25
Repeat with another cake layer and filling; top with the remaining cake layer.
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26
Cover the entire cake with plastic wrap, and carefully transfer to the refrigerator, steadying it with your hands to keep the layers from sliding.
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27
Chill until filling is firm, at least 2 hours.
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28
When ready to serve, frost the cake and garnish with poppy seeds.
