Preheat oven to 350°F. Spray two 9-inch cake pans with nonstick cooking spray, line the bottom of the pans with parchment paper and set aside.
In a large mixing bowl, whisk together the cake flour, baking powder, and salt. Set aside.
Combine the buttermilk and vanilla extract in a measuring cup and stir until well combined. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl using an electric mixer, cream together the butter and sugar for about 4-5 minutes or until light and fluffy.
Add the dry ingredients to the creamed butter and sugar in three additions alternating with the buttermilk mixture (begin and end with the dry ingredients) on low speed. Mix in each addition until just combined, making sure not to over mix the batter.
In a separate clean mixing bowl, beat the egg whites to stiff peaks. Gently fold half of the egg whites into the batter, then fold in the remaining egg whites until just combined.
Pour the cake batter into the prepared cake pans and spread around into one even layer. Gently tap the cake pans on the counter a couple times to release any air bubbles.
Bake at 350°F for 28-32 minutes or until a toothpick inserted into the center of the cakes comes out clean. Remove from the oven and allow to cool in the pan for about 20 minutes, then remove the cakes from the pans and transfer to a wire rack to cool completely.