Preheat & Prep: Preheat the oven to 350°F. Grease and line three 8inch cake pans with parchment paper.
Mix Dry Ingredients: In a bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
Beat Wet Ingredients: In a large bowl or stand mixer, beat butter, oil, and sugar for about 2 minutes until light and fluffy. Use a paddle attachment for a stand mixer or a hand mixer.
Add Eggs: Add eggs one at a time, beating well after each addition. Scrape the bowl as needed.
Add Vanilla: Mix in the vanilla extract.
Combine: Add a third of the buttermilk, mix on low. Add a third of the dry ingredients, mix on low. Repeat until all the buttermilk and dry ingredients are combined, finishing with the dry ingredients. Be careful not to overmix.
Divide & Bake: Pour the batter into the prepared pans and bake for about 30 minutes until a toothpick comes out clean.
Cool: Let the cakes cool in the pans for 10 minutes, then transfer to a rack to cool completely. If not using the same day, wrap in plastic and refrigerate or freeze.