Preheat the oven to 350°F. Butter or spray two 9-inch round cake pans and line the bottom of each pan with a round of parchment paper.
Whisk together the cake flour, baking powder and salt. Set aside.
Whisk together the buttermilk, egg whites, and vanilla in a medium bowl. Set aside.
In mixer with paddle attachment, or with a hand mixer, beat butter and sugar at medium speed for a full 3 minutes, until the mixture is very light.
Reduce speed to low and gradually add half of the dry ingredients and half of the wet ingredients. When combined add the remaining dry and wet ingredients. Beat until combined, scrape down side of bowl if needed. Beat two minutes more on medium speed to aerate the batter.
Divide the batter between the two pans and smooth the tops with a rubber spatula.
Bake for 30-35 minutes, or until the cakes are well risen and springy to the touch – a thin knife inserted into the centers should come out clean.
Transfer the cakes to cooling racks and cool for about 5 minutes, then remove from pans, peel off parchment, and let cool completely.
Cream Cheese Frosting
Using the paddle attachment, beat the cream cheese, sifted powdered sugar, and vanilla until smooth and creamy. Remove to another bowl and clean out mixing bowl.
Switch to the whisk attachment and beat the heavy cream at medium-high until stiff peaks form.
Gently fold the whipped cream into the cream cheese mixture. When most of the cream cheese and whipped cream are incorporated, whisk the frosting together to make smooth, about one minute.
Place one cake layer onto a plate and spread 1/2 - 3/4 cup of the frosting on top. If you prefer more frosting in the middle, feel free to add more!
Place the second cake layer on top of the first, and frost the top and sides of the cake.
I use cake flour, but if you don't have any you can use all purpose flour by following this calculation. Replace 1 cup of cake flour with 1 cup all purpose flour MINUS 2 tablespoons all purpose flour PLUS 2 tablespoons of cornstarch.
If you don't have buttermilk, you can add 1 tablespoon of white vinegar or lemon juice plus enough milk to measure 1 1/4 cups.