Preheat the oven to 350°F. Grease and flour the pan 2 8” or 9” pans or brush with homemade cake release. Whisk together the flour, baking powder, baking soda and salt in a medium bowl. Set aside.
Cream together the butter, oil, and sugar in a large mixing bowl with an electric mixer until light and fluffy. Add vanilla and then the eggs, one at a time, beating well after each addition and stopping to scrape the sides and bottom of the mixing bowl once or twice.
Add one-third of the flour mixture, mixing at low speed until incorporated. Add the sour cream and mix until well combined. With mixer on low speed, add another third of the flour mixture, and mix until combined. Add the milk and mix to incorporate, scraping side and bottom of bowl. Add the remaining flour and mix until everything is well combined. The batter will be thick and fluffy.
Allow batter to rest for about 5-10 minutes.
Pour the batter into the prepared pans, dividing the batter equally. Bake at 350°F for 28-32 minutes or until toothpick inserted in center comes out clean. You might notice edges are just starting to separate from pan. Remove from the oven and set on cooling racks.
Allow the layers to cool for about 10 minutes in the pans before turning out onto cooling racks. Cool completely before frosting.
Once ready to assemble, level each layer to remove any dome. Set the first layer, crust side down, and frost with your chosen frosting or buttercream. Add the second layer and frost the top and sides.