Preheat the oven to 325 degrees. Grease and flour three 8x2 inch round cake pans. Place a piece of parchment cut to the size of the pan in the bottom of each.
Put the first 5 ingredients into the bowl of your mixer. Mix on low speed for at least 30 seconds to combine.
Add the softened butter (cut into pieces) mix on low speed just until it looks like coarse sand. The dry ingredients will be moistened/coated by the butter and will stick to together if you press some between two fingers. Don't over-mix or it will turn into a large dough-like ball.
Add the eggs 1 at a time, mixing until blended.
Add the vanilla to the 1 ¼ cup buttermilk. With the mixer on lowest speed gradually pour into the mixer. Increase the speed to #2 or # 3 (on a KitchenAid mixer). Mix for 2 minutes. Batter will be fluffy and smooth. If you are using a hand mixer rather than a stand mixer, you will need to mix a bit longer.
Divide batter evenly between your three prepared (8 inch) pans.
Bake at 325 degrees for 25 to 30 minutes. Cool for 5 minutes and turn out of pans.