Preheat the oven to 325 degrees F. Spray two 8-inch round cake pans with non-stick spray, line the bottom parchment paper, and spray again. Set aside.
In a medium size bowl, whisk together the cake flour, baking powder, and salt. Set aside.
In the bowl of a stand mixer, fitted with the paddle attachment, beat the butter, sugar, and oil on medium-high until fluffy and smooth, about 3 to 5 minutes.
With the mixer on medium speed, add the eggs and the egg whites, one at a time, making sure to scrape down the sides and bottom of the bowl along the way. Turn the mixer to medium-high and continue to beat for an additional 2 to 3 minutes, until the mixture is smooth and fluffy. Stir in the vanilla.
Turn the mixer on low and add 1/3 of the flour mixture to the butter mixture and mix until fully incorporated. Then add half of the buttermilk, followed by another 1/3 of the flour mixture, the second half of the buttermilk and lastly, add the remaining flour mixture and mix until incorporated.
Fold in the sour cream, followed by the sprinkles.
Evenly distribute the cake batter among the two cake pans (about 24 ounces in each) and bake for 30 to 35 minutes, until toothpick comes out with just a few moist crumbs on it.
Remove cakes from the oven and let cool in pans for 15 minutes before inverting onto cooling racks.
When cakes are completely cooled, divide each cake in half horizontally, so you have four layers. You can then wrap the cake layers in plastic wrap to freeze until you’re ready to decorate.