Make the White Cake. Preheat the oven to 350F and grease 3 8-inch round cake pans and line with parchment paper to ensure the batter doesn't stick. Set aside.

In a large mixing bowl, sift and whisk together the flour, baking soda, baking powder, and salt. Set aside.

Beat the butter, oil, and sugar with a mixer on medium-high speed until smooth and creamy, about 2 minutes. Then, mix in sour cream, vanilla extract, vanilla extract.

On low speed, add about a third of the flour mixture and a third of the milk, alternating until all of the flour and milk is added to the batter. Be sure not to over mix the batter — a few lumps are okay.

In a separate bowl, whip the eggs whites together on high speed until they form foamy peaks, about 3-4 minutes. Then, add the whipped egg whites to the batter and carefully fold them into the batter, scraping the bowl as needed.

Next, evenly divide the batter in the 3 prepared pans. Bake for 20-25 minutes or until a toothpick comes out clean. Note, baking time may vary depending on your oven. Be sure not to overbake or your cake will be dry. Once done, allow the cakes to cool in the pan on a wire rack until completely cooled.

Make the Frosting. In a large bowl, beat the softened butter on high until smooth and creamy. Next, mix in vanilla extract paste, salt, and gradually add the powdered sugar, mixing on low speed at first to prevent a sugar cloud. When the sugar is pretty much incorporated, beat the frosting for about 2 minutes on high or until smooth. You should have enough frosting to decorate.

Assemble Cake. Place the first layer of cake on a serving plate or cake stand, and evenly spread the top of the cake layer with frosting. Next, add the second and third layers and repeat. Once the last layer is on top, frost the top and sides of the cake. Then, using the extra frosting, decorate by piping swirls or flowers on the cake. Refrigerate the cake for at least 20-30 minutes before slicing. Then, enjoy!