In a stand mixer with the paddle attachment, beat the butter and sugar together until light and fluffy.
Add the vanilla, then the egg yolks and whole eggs one at a time until incorporated.
In a separate bowl, whisk together the flour, baking powder, and salt.
With the mixer running, add the flour mixture in increments, alternating between that mixture and the buttermilk. Begin and end with the flour mixture.
Gently fold in the chopped pecans until incorporated, but don't overmix.
Divide the batter between 2 prepared 8" cake pans. Bake for about 50 minutes at 350 degrees Fahrenheit, or until a toothpick inserted in the center comes out clean.
Let cool completely before turning out of the pans. Once cool, use a large serrated knife to cut the domed tops off of each cake and discard. Then carefully cut each whole layer in half so you have 4 layers.