PERFECT PARTY CAKE

FOR THE CAKE:

2 1/2 cups cake flour

1 Tablespoon baking powder

1/2 teaspoon salt

1 1/4 cups buttermilk

4 large egg whites

1 1/2 cups granulated white sugar

2 teaspoons freshly grated lemon zest

1/2 cup (1 stick) unsalted butter, at room temperature

1/2 teaspoon pure lemon extract