For the cake:
- 2 1/3 cups (or 9 1/4 oz if using a scale, as I did) cake flour, plus more for cake pans
- 2 3/4 teaspoon baking powder
- 1/4 teaspoon salt
- 1 3/4 cups granulated sugar, divided
- 2 tablespoons lemon zest
- 3/4 cup (6 oz, or 1 1/2 sticks) unsalted butter, room temperature, plus more for cake pans
- 1 cup milk, room temperature
- 5 egg whites, room temperature
- 1/4 teaspoon cream of tartar
- 1 cup lemon curd, chilled
For the frosting:
- 1 cup (8 oz, or 2 sticks) unsalted butter, room temperature
- 2 tablespoons lemon zest
- 3 1/2 cups powdered sugar
- 3 tablespoons fresh lemon juice
- Heat oven to 350 degrees F. Generously butter bottom and sides of 2 8-inch round cake pans. Dust with flour, then turn pans upside down and tap bottoms of pans to release excess flour.
- In a large bowl, whisk cake flour, baking powder and salt until well combined.
- In a food processor, pulse 1/4 cup sugar with lemon zest until well combined.
- In the bowl of a stand mixer fitted with paddle attachment or in a large bowl using an electric hand mixer, beat butter and lemon sugar on medium speed 1 1/2 minutes until light and fluffy. Add remaining 1 1/2 cups sugar and beat 1 1/2 minutes until smooth.
- On low speed, stir in flour mixture and milk alternating in batches, starting and ending with flour mixture. Scrape sides of bowl with a spatula and stir until just combined.
- In another large bowl with a clean electric hand mixer, beat egg whites on medium speed until foamy. Add cream of tartar and beat on medium-high speed 1 to 2 minutes until stiff peaks form.
- Carefully fold one-quarter of egg white mixture into cake batter just until combined. Add remaining egg white mixture, a quarter at a time, folding in after each addition until just combined.
- Divide batter evenly among prepared cake pans. Bake 35 minutes until a toothpick inserted in centers comes out clean. Cool cakes 10 minutes in pans, then gently invert cakes onto a cooling rack to cool completely.*
- When cakes are completely cooled, use a long serrated knife to slice each cake in half horizontally (so you end up with 4 thin cake layers). Gently slice off any domed tops from cake layers, if needed.
- Place one layer, cut side down, on a serving plate. Spread 1/3 cup lemon curd on top in an even layer; top with another cake layer. Spread another 1/3 cup lemon curd on top in an even layer. Top with another cake layer. Spread remaining 1/3 cup lemon curd on top in an even layer, then top with final cake layer, cut side down.
- Make the frosting: In the bowl of a stand mixer fitted with paddle attachment or in a large bowl with an electric hand mixer, beat butter and lemon zest until light and fluffy. Add powdered sugar in a few batches, stirring at first then increasing to medium speed just until combined. Add lemon juice and beat just until combined.
- Use an offset spatula to frost tops and sides of cake. Let frosting set a while before serving.
- *NOTE: At this point, I covered the cooled cakes with plastic wrap and let them chill in the fridge for a few hours so they’d be easier to cut/handle/frost, but you can also proceed with the recipe without chilling the cakes.