Preheat oven to 350°. Spray 2 (9-inch) round deep cake pans with baking spray with flour. Line bottom of pans with parchment paper, and spray pans again.
In a large bowl, beat butter and sugar with a mixer at medium speed until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add egg yolks, one at a time, beating well after each addition. In a medium bowl, whisk together Swans Down® Cake Flour, baking powder, and salt. With mixer on low speed, gradually add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture, beating just until combined after each addition. Beat in vanilla.
In a large bowl, using clean beaters, beat egg whites with a mixer at high speed just until stiff peaks form. Stir one-fourth of egg whites into batter. Gently fold in remaining egg whites. Divide batter between prepared pans.
Bake until a wooden pick inserted in center comes out clean, about 30 minutes. Let cool in pans for 10 minutes. Remove from pans, and let cool completely on wire racks. Spread Vanilla-Buttermilk Frosting between layers and on top and sides of cake. Garnish with raspberries and mint, if desired.
Makes 1 (9-inch) cake
In a large bowl, beat butter with a mixer at medium speed until creamy. Gradually add confectioners’ sugar and enough buttermilk to achieve a spreadable consistency. Beat in vanilla and salt.
Makes about 6 cups