Preheat oven to 325 degrees. Butter cake pans, and line each with a parchment-paper circle cut to size. Butter and flour parchment; set pans aside. Sift together flour and baking powder 3 times; set aside.Advertisement
In the bowl of an electric mixer fitted with the paddle attachment, cream butter and sugar together until fluffy. Add egg yolks one at a time, beating until incorporated after each. Add flour mixture to egg mixture in 3 additions alternately with milk, starting and ending with flour.
In the clean bowl of an electric mixer fitted with the whisk attachment, beat egg whites with salt until stiff but not dry. Mix 1/4 of the whites into the batter, and then fold in remaining whites.
Pour the batter into pans (see batter amounts and baking times, under ingredients). Bake until tops are golden brown and a tester inserted into centers comes out clean. Cool cakes in pans for 20 minutes. Run a knife around outside of cakes. Turn out onto wire racks, remove papers, and re-invert cakes to cool, top side up. Wrap cooled cakes in plastic; refrigerate at least overnight before using.
Approximate batter amounts and baking times: Each 7-inch round cake (make 3), 4 cups batter, 65 minutes baking time; each 10-inch round cake (make 2), 7 cups, 1 hour 15 minutes; each 14-inch petal cake (make 2), 11 cups, 65 minutes; each 16-inch round cake (make 2), 18 cups, 1 hour 25 minutes. All cakes should be just over 2 inches high after baking.