Preheat oven to 350°F. Grease three 8-inch round pans with baking spray.

In a stand mixer fitted with the paddle attachment, beat the butter, oil, sugar, and vanilla on medium-high speed for 4–5 minutes, until very pale, light, and fluffy. Scrape down the bowl 2–3 times, this step builds your cake’s structure.

Before adding the eggs, emulsify them with an immersion blender, this helps break down the proteins and evenly distribute the fat, creating a smoother batter and a finer crumb. If you don’t have an immersion blender, just whisk the eggs together until well combined. Add the eggs to the creamed mixture one at a time, mixing well after each addition. The batter should be smooth and slightly thick.

In a separate bowl, whisk together the cake flour, baking powder, baking soda, and salt.

With the mixer on low speed, add the dry ingredients in three additions, alternating with buttermilk in two additions, beginning and ending with the dry. Mix just until incorporated; do not overmix or the crumb will toughen.

With the mixer still on low, mix in the sour cream until fully combined and silky. The batter will be thick, smooth, and velvety.

Evenly divide the batter between the prepared pans and smooth the tops with a spatula. Bake for 25–30 minutes, until the tops are lightly golden and a toothpick inserted in the center comes out with a few moist crumbs. Start checking around 25 minutes, over baking dries the crumb quickly.

Let the cakes rest in the pans for 10 minutes, then invert onto a wire rack. Cool completely before frosting. Wrap cooled layers tightly. If assembling later, they stay fresh up to 3 days refrigerated or up to 2 months frozen