Preheat the oven to 350°F/175°C and grease 2 8-inch cake pans. Set aside.
In a large bowl, whisk flour, baking powder, baking soda and salt together to combine. Set aside.
In a large mixing bowl using an electric hand mixer (or stand mixer), beat the butter, oil and sugar on medium speed for 6 minutes until fluffy and light. Scrape the sides of the bowl. Add eggs, one at a time, beating well with each addition. Scrape down the bowl as needed. Add vanilla extract and beat until combined.
On a medium speed, using the mixer to alternate adding flour mixture and buttermilk to the butter mixture in 3 additions, starting with flour mixture as in order: flour-buttermilk-flour. Beat until just combined after each addition. The batter should be smooth and completely incorporated. Avoid overmixing.
Divide batter evenly into your prepared cake pans and bake on the center rack for 30-35 minutes, until the cake tester (or a toothpick) comes out clean.
Allow the cake to cook in cake pans for 10-15 minutes before transferring to cool completely on a wire rack. The cake must be cooled completely or chilled in the fridge for at least 1 hour before applying frosting.