Preheat the oven to 350 degrees F.
Grease 3 9" cake pans with cooking spray and line the bottom with parchment paper. To do this, set your cake pan on a sheet of parchment paper and trace it with a marker. Cut it out. Repeat two more times for all three cake pans.
In a large bowl with an electric mixer, add the butter and granulated sugar.
Beat until well combined, about 2-3 minutes.
Add the eggs, one at a time, beating until combined.
Add the vanilla, and beat until combined.
In a separate large bowl, whisk together the flour, baking powder, baking soda, and salt.
Add ⅓ of the flour to the butter mixture. Stir it in with a rubber spatula.
Add ½ of the buttermilk, stirring with the rubber spatula until just combined.
Repeat with the remaining flour and buttermilk, ending with the flour mixture. Don't over mix!
Divide the batter among the three pans.
Bake in the preheated oven for 27-29 minutes, until the tops are slightly golden and a toothpick comes out of the middle clean.
Cool in the pan for about 5 minutes and then invert each pan onto a cooling rack to cool completely. Be sure to run a knife around the edges of the cake pans before inverting them.