Preheat your oven to 350 degrees F. Grease flour two 8-inch round cake pans then dust them with flour. The flour will help the cake batter climb up the pan and get nice and tall. It also helps make the baked cake very easy to pop out.
Add the cake flour, sugar, salt, baking powder and baking soda to the bowl of a stand mixer and blend together with a paddle attachment.
Add the softened butter to the bowl and mix until the butter is blended into the dry ingredients and the mix looks like coarse sand.
Add ½ cup of buttermilk and the ½ cup of oil to the bowl of the mixer and mix on medium speed for two minutes. The batter will be very thick and stiff.
In a separate small bowl, mix the remaining ¾ cup buttermilk, egg whites, vanilla and pink gel food coloring. Whisk this mix a little bit by hand just to break up the egg whites.
Turn your stand mixer on low speed and very slowly pour the pink egg mix into the bowl, letting the wet ingredients blend into the flour mix evenly. Mix until the batter is smooth and be sure to scrape down the sides of the bowl to ensure there are no lumps.
Divide the cake batter between the two prepared cake pans and then bake in the preheated oven for 35 to 40 minutes. Stick a toothpick in the center of each cake to check that they are fully baked. The toothpick should come out clean and with no sticky batter when the cakes are done.
Let the cakes cool inside the pan for about ten minutes before flipping them out on a cooling rack.
Make the vanilla buttercream by beating the butter and powdered sugar in a stand mixer with a paddle attachment until the butter is very light and fluffy. It should be almost white.
Add the milk and vanilla to the bowl and blend into the frosting to make it soft.
Spread about 1 ½ cups of frosting over the top of one of the cake layers. Place the second cake layer on top of the first, sandwiching the frosting inside the cake. Use an offset metal spatula to coat the outside and top of the cake with a small amount of frosting. You just want enough frosting to stick the cakes together and make the outside smooth. This is called a crumb coat of frosting as it traps all the cake crumbs. Place the cake in the fridge for about 30 minutes to let the frosting harden.
Remove the cake from the fridge and use an offset metal spatula to add the rest of the vanilla frosting to the outside of the cake. Decorate as you wish and then enjoy the pink velvet cake!