Preheat oven to 350 degrees F. Grease and flour two 9x2 inch round cake pans.
Cream the butter in bowl of a stand mixer fitted with a paddle attachment. Add sugar and continue beating until light, scraping bowl often. Add the salt and continue creaming for another 5 minutes at medium high speed.
While the butter and sugar are creaming in the stand mixer, sift flour and baking powder together. Remember, the flour should have already been sifted before measuring. Set aside in a bowl.
Combine the eggs and yolks together in a separate bowl.
Combine the milk and vanilla in a measuring cup.
When the creamed mixture start to look fluffy, add the egg/yolk mixture gradually, making sure mixture comes together fully after each addition. Scrape down bowl and continue mixing until uniform.
By hand or with very lowest speed of mixer, add the flour mixture and milk mixture alternately, beginning with flour and ending with flour so that you add dry, wet, dry, wet, dry. When all flour and liquid is incorporated and batter appears uniform, divide batter among the pans.
Bake at 350 degrees F until done. My cake was done in about 28 minutes, but all ovens are different so check at 18 min.Cake is done when middle bounces back and/or small sharp knife inserted in center comes out clean and sides pull away from pan.