Cream butter; gradually add sugar, beating well. Add egg yolks, one at a time, beating well after each addition.
Combine flour, baking powder, and salt; add to creamed mixture alternately with milk, beginning and ending with flour mixture. Mix well after each addition. Stir in vanilla.
Beat egg whites (at room temperature) until stiff peaks form. Gently fold into batter.
Pour batter into 2 greased and floured 9-inch round cake pans. Bake at 325° for 40 to 45 minutes or until a wooden pick inserted in center comes out clean. Cool in pans 10 minutes; remove layers from pans, and let cool completely.
Spread frosting between layers and on top and sides of cake. Garnish with pecan halves.