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1
Preheat oven to 350F; position rack in middle of oven.
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2
Crease and flour two 8x2-inch round cake pans.
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3
Sift flour, baking powder and salt together.
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4
Pulse 1/4 cup of the sugar with the zest in a food processor until well combined.
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5
Beat the butter and lemon sugar in a mixer until light and fluffy-1 to 2 minutes.
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6
Add remaining 1 1/2 cups sugar and beat until smooth.
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7
Beat in 1/4 of the milk until just blended.
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8
On low speed, add flour mixture alternating with remaining milk in 3 batches, scraping as needed.
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9
Beat until just blended.
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10
In a clean bowl, whip egg whites on medium speed until foamy, add cream of tartar, increase speed to high, beat until whites just hold stiff peaks.
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11
Add 1/4 of the whites to batter and fold in with a whisk or spatula.
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12
Fold in remaining white 1/4 at a time.
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13
Divide batter evenly between cake pans and smooth tops.
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14
Bake until tester in center comes out clean- about 35-40 minutes.
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15
Let cool for 10 minutes, remove from pans and cool completely on rack.
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16
Cut each cake in half horizontally using a long serrated knife.
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17
Place one layer on a serving plate, cut side up.
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18
Spread with 1/3 cup of chilled lemon curd.
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19
Lay another cake layer on top, spread with lemon curd and repeat with 3rd layer.
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20
Top with fourth cake layer.
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21
Up to a few hours before serving, spread a thin layer of frosting on cake, filling gaps as you go.
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22
Chill to firm crumb coat for about 30 minutes.
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23
Spread remaining frosting decoratively over sides and top of cake.
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24
Scatter top with lemon zest as garnish.
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25
TO MAKE FROSTING: In an electric mixer, beat butter and lemon zest until light and fluffy.
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26
Add confectioners sugar in batches and beat until light and fluffy.
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27
Add lemon juice and beat for 1 minute.
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28
Can be made a couple of hours ahead and kept covered at cool room temperature.
