Preheat the oven to 350° F. Grease and flour a 9-inch round and an 8-inch round baking pan or spray with nonstick cooking spray. Set aside.
In a large bowl, beat oil, eggs, and sugar until well combined. Add sour cream and vanilla and blend well.
In a separate bowl, whisk together flour, baking powder, and salt. Alternate adding flour mixture with milk in two additions, beating just until combined. Don't overmix.
Pour cake batter into prepared pans, about ¾ full. Bake for about 40-45 minutes, or until cake springs back when lightly touched, or toothpick inserted into center comes out clean.
Place cakes in pans on wire rack to cool for 15 minutes, and then remove from pans and allow to cool completely before frosting and decorating.