Preheat oven to 350° and line 3 9" cake pans with parchment and nonstick spray.
In the bowl of an electric mixer, add flour, sugar, baking powder, salt and cocoa powder.
In a separate bowl, combine the oil, eggs, buttermilk, vanilla extract, and vinegar.
With the mixer on low speed, slowly stream in the wet ingredients.
Stop the mixer and scrape the bowl, making sure all dry ingredients are incorporated.
Turn the mixer to medium high speed and mix for 4 minutes.
Evenly distribute the batter into 3 9" cake pans, and then bake for 25-30 minutes, or until the top of the cake springs back when touched.