Place the butter into a medium saucepan over medium heat. Let the butter cook while occasionally stirring to ensure the butter is cooking evenly.
Cook the butter until it is a deep golden brown color and smells nutty and toasted, about 5 -7 minutes. Remove the pan from the heat.
Let the butter cool to room temperature, until it is solid, but scoopable. Similar in texture to room temperature butter.
Preheat the oven to 335F. Prepare your cake pans. Brush the bottoms and sides of a 9x13 cake pan with melted butter. Line the bottoms and sides with parchment paper.
Combine the buttermilk, oil, eggs, and vanilla in medium bowl. Whisk to thoroughly combine.
In the bowl of a stand mixer, combine the cake flour, sugar, baking powder and salt. On low speed, mix for 1 minute.
With the mixer still running, add in the softened butter chunks, one or two pieces at a time. Mix until the mixture resembles cornmeal. You should be able to gather a bit in your hand, squeeze and you have a solid piece. This means the butter is evenly distributed.
With the mixer still on low, pour in the 4oz/½ cup of the wet ingredients and mix until the flour mixture is moistened.
Turn the mixer speed to medium (4 or 6) and whip for *two full* minutes. The mixture should be whipped up, thick, and lighter in color.
Scrape the sides and bottom of the bowl to ensure everything is properly mixed.
With the mixer speed on low, add the remaining wet ingredients in three parts, scraping down the bowl after each addition has been mixed in.
Once all the wet ingredients have been added, give the bowl a final scrape and mix with a spatula. Pour the batter into the pan. Spread the batter evenly in the pan.
Bake the layers for 40-50 minutes. Start checking the cake at minutes to test for doneness. If a toothpick comes out clean, and the top of the cake feels springy and set when touched, take the cakes out.
Cool the cake for 15 minutes in the pan.
Run a palette or butter knife around the cake in the pan before turning them out to cool completely on cooling racks.
Wrap in plastic wrap and chill in the refrigerator a couple hours.