Preheat the oven 350°F. Lightly grease two 9 inch round cake pans with baking spray. Place a parchment paper circle in the bottom of each pan. Spray the parchment with baking spray. Set aside.
Whisk together the flour, baking powder, baking soda and salt in a medium size bowl.
Add the oil and butter to the bowl of a stand mixer (or a large bowl if using a hand mixer). Beat together until fully combined.
Beat in the granulated and brown sugar on medium speed for 3 minutes or until fully combined.
Add the vanilla extract and mix until combined.
Next, add the eggs, one at a time, until completely incorporated.
Add the dry ingredients and the buttermilk, alternating between the two, scraping down the sides of the bowl as necessary. (Stir in half of the dry ingredients, then half of the buttermilk and then repeat.)
Evenly divide the batter between the prepared cake pans. Smooth the top with an offset spatula.
Bake the cakes for 22 to 27 minutes or until an inserted toothpick comes out clean. Let the cakes cool completely in the pan.
Carefully remove the cakes from the pans and place on a level surface. Use a large serrated knife to cut any doming or uneven parts of the cake if there are any.
Place one of the cakes on your cake stand or plate. Set aside.