How to Make It
Preheat oven to 350°. Grease and flour 3 (8-inch) round cake pans.
Whisk together flour, baking powder, and salt in a medium bowl. Set aside.
Beat butter and sugar together at medium speed with an electric mixer until light and fluffy, about 5 minutes. Mix in vanilla.
Whisk together milk and egg whites in a separate bowl until just combined.
Gradually add flour mixture and milk mixture alternately to butter mixture, beginning and ending with flour mixture, mixing at low speed until just combined. Scrape the bowl well with a rubber spatula, as needed.
Divide batter evenly between prepared pans. Bake cakes on middle rack at 350° for 30 to 35 minutes, or until a toothpick inserted into the center of each cake comes out clean. Cool in pans on wire racks 10 minutes; remove cake layers from pans and cool completely on wire racks, about 1 hour.
Wrap cake layers individually in plastic wrap; freeze for 4 to 6 hours. (This step is optional, but frozen layers are easier much easier to work with. We recommend freezing for at least one hour when making a naked cake to ensure that crumbs don’t break off into the icing.)
When ready to frost the cake, remove layers from freezer and unwrap. Level any uneven layers with a serrated knife if necessary.
Prepare Vanilla Buttercream frosting.
Place a dollop of frosting in the center of a cake stand or serving plate (to keep the cake from sliding) and place 1 cake layer on top of frosting. Spoon about 1 cup of frosting directly on top of first layer; using an offset spatula, spread the frosting evenly over the top and just past the edges of the first layer. Place the second cake layer upside-down directly on top of the first layer; repeat frosting process. Place the third cake layer on top of the second layer. Spoon about 1 1/2 cups of frosting directly on top of third layer, and lightly frost the entire cake, starting with the top and moving down the sides, leaving the layers largely exposed. Place the assembled cake back in the freezer for 20 minutes to allow the icing to set. Decorate as desired.