1 1/2 cups unsalted butter, softened
2 cups sugar
6 large eggs, at room temperature
3 cups all-purpose flour
1 1/2 teaspoons baking powder
1/2 teaspoon baking soda
1/2 teaspoon salt
1 cup whole buttermilk
Lemon Curd Filling, recipe follows
Vanilla Buttercream, recipe follows
Candied Citrus Zest, recipe follows
Preheat oven to 325°. Spray 3 (9-inch) cake pans with nonstick baking spray with flour. Line bottoms of pans with parchment rounds. Spray again, and set aside.
In a large bowl, beat butter and sugar at medium-high speed with an electric mixer until fluffy, about 5 minutes. Reduce mixer speed to low. Add eggs, one at a time, beating well after each addition, and scraping down sides of bowl as necessary.
In a medium bowl, sift together flour, baking powder, baking soda, and salt. Add flour mixture to butter mixture in thirds, alternating with buttermilk, beginning and ending with flour mixture. Divide batter evenly among prepared pans. Tap pans against counter to release any air bubbles.
Bake until tops are golden and a wooden pick inserted in center comes out clean, 25 to 30 minutes. Cool in pans 10 minutes. Remove from pans, and cool completely on wire racks.
Once cooled, wrap tightly with plastic wrap, and freeze at least 2 hours. Remove plastic wrap, and spread layers with Lemon Curd Filling. Frost top and sides of cake with Vanilla Buttercream. Garnish with Candied Citrus Zest.