Preheat oven to 350 degrees F.
Grease and flour two 8" round cake pans.
In a bowl, add the cake flour, baking powder, baking soda and salt. Whisk and set aside.
In another bowl, add the buttermilk, oil and vanilla. Whisk well and set aside.
In a large mixing bowl, beat the butter and sugar with an electric mixer set on medium-high for several minutes until light and fluffy.
Add the whole eggs, one at a time, mixing on medium just until combined after each addition.
Next add in the egg yolks and mix on medium just until combined.
Now alternate adding in the dry and liquid mixtures.( Add in a third of the dry mixture and mix on medium just until combined. Add in half of the liquid mixture and mix on medium just until combined. Add in another third of the dry mixture and mix on medium just until combined. Add in the other half of the liquid and mix on medium just until combined, then finally the last third of the flour mixture and mix only until combined.) Be very careful not to mix too long after each addition or this will make your cake very dense. Only mix until the ingredients are incorporated. Scrape down the sides of the bowl and mix again on medium just for about 10 seconds or until everything is well combined. Be really careful not to over-mix the batter.
Pour into two greased and floured 8" round pans and spread evenly.
Bake at 350 for about 35 minutes.
Test for doneness with a toothpick. There should be some light crumbs on the toothpick, but nothing liquid. Be careful not to overbake this cake or it could come out dry. The tootphick does not have to come out clean. It should have some moist crumbs on it, but no raw batter.
Cool cake layers in their pans, on a cooling rack, for about 15 minutes. Then turn out of the pans and directly onto the racks and cool completely before adding the fudge frosting.