6ouncesunsalted butter, softened but slightly cool(170 grams)
1 ¾cupsgranulated sugar, divided use (1 ½ and ¼)
2tablespoonslemon zestlightly packed and finely grated
1cupwhole milk, room temperature(230 grams)
1teaspoonvanilla extract
5largeegg whitesat room temperature
¼teaspooncream of tartar
Filling
1 -1 ½cupslemon curd
Frosting
8ozunsalted butter, softened
2tablespoonslemon zest
3 ½cupssifted confectioners' sugar
3tablespoonsfresh lemon juice
1-2tablespoonsof milk or as needed
1pinchsalt or to taste
Instructions
Preheat oven to 350ºF. Spray three 8 by 1 ½ inch round cake pans or two 8x2 inch round cake pans with flour-added baking spray or just grease generously and dust with flour.
Mix the flour, baking powder and salt together in a medium size bowl and set aside.
In the stand mixing bowl, beat the softened butter until creamy, then add 1 ½ cups sugar and beat until light and fluffy. Add a little of the milk and beat just until blended.
With the mixer on low speed, add flour mixture alternating with remaining milk in 3 batches, scraping sides of the bowl.
In a second mixing bowl, whip egg whites on medium speed until foamy, add cream of tartar. Increase speed to high, beat, gradually adding the remaining ¼ cup of sugar until whites just hold stiff peaks.
Add some of the whipped whites to batter to lighten, then fold in remaining whites gradually. Divide batter evenly between cake pans and smooth tops. Bake for about 28 minutes or until tops are brown and a toothpick inserted comes out clean.
Let cool for 10 minutes, remove from pans and let cool completely on rack.
Spread the top of two cakes (or one if you only made two layers) with lemon curd and stack so that you have three layers and two levels of lemon curd filling. Let cake stand for about 30 minutes while you make the frosting.
Frosting: In an electric mixer, beat butter and lemon zest until light and fluffy. Add confectioners’ sugar gradually and beat well. Add lemon juice and beat for 1 minute. Add milk as needed until you get a creamy, spreadable consistency. I recommend adding a little salt as well. If you used salted butter there will be no need, but with unsalted butter it's sometimes a good idea to balance with a pinch or two.