The fluffy exterior of this cake conceals a delicious pink filling, made simply by combining some of the frosting with raspberry jam.
Preheat oven to 350 degrees. Butter two 8-by-2-inch professional round cake pans, and line the bottom with parchment rounds. Butter the parchment, and dust pans with flour, tapping out any excess; set aside.
Sift together the cake flour, baking powder, and salt into a medium bowl, and set aside. Beat the butter in the bowl of an electric mixture fitted with the paddle attachment until it is creamy. Add the sugar to the butter in a steady stream, and continue beating until the butter is light and fluffy, about 3 minutes. Reduce speed to low, and add dry ingredients alternately with the milk and vanilla in three additions, starting and finishing with the dry ingredients; be careful not to overmix. Set batter aside.
In a medium metal bowl or clean bowl of an electric mixer, whisk egg whites just until stiff peaks form. Fold one-third of the egg whites into the batter until combined. Fold in remaining whites in two batches. Divide batter between prepared pans, and smooth tops with a metal spatula. Bake until a tester inserted near the center comes out clean and the cake springs back when pressed lightly in the center, about 30 minutes. Let pans cool 15 minutes on a wire rack before unmolding. Loosen the sides with a small metal spatula or paring knife, and invert onto greased wire racks. To prevent the layers from splitting, invert again so that the tops are up. Cool completely before assembling cake or wrapping airtight to freeze cake for later.
If cakes are not level, use a serrated knife to trim tops off. Carefully slice each cake horizontally into two equal layers. (You will have four layers.) Place one-third of the frosting in a bowl, and fold in raspberry jam.
To assemble, place one sliced layer on an 8-inch cardboard cake round. Spread the top with 1/4 inch of raspberry frosting. Repeat with remaining layers and remaining raspberry frosting, placing the final layer bottom side up. Lightly coat the assembled cake with a thin layer of white frosting to protect against crumbs in the frosting. Finish with remaining frosting. Serve immediately, or keep refrigerated until ready to serve.