Preheat the oven to 350°F (175°C). Grease and flour two 9-inch cake pans, then line the bottoms with parchment paper. Set these aside proudly.
In a small bowl, mix your egg whites and 1/4 cup of buttermilk together. It’s a lovely sight! Set that aside as well.
In a mixing bowl, beat the softened butter and granulated sugar until creamy, about 2-3 minutes. Add your vanilla extract and give it a good mix. Gradually add the dry ingredients—cake flour, baking powder, and salt—mixing until everything is well combined.
Slowly add your egg white mixture to the batter, beating until everything is nicely incorporated. Then, beat in the remaining buttermilk. Continue for an additional 1-2 minutes until the batter is delightfully fluffy.
Divide the batter evenly between your prepared cake pans. Pop those in the preheated oven and bake for 25-28 minutes, or until you can poke a toothpick into the center and it comes out clean. Once done, allow them to cool in the pans for 5 minutes before transferring them to a wire rack to cool completely.
While the cakes are cooling, prepare the frosting. In a mixing bowl, beat the softened butter for 3-4 minutes until pale in color. Gradually add the powdered sugar, vanilla extract, and milk, beating until the frosting is smooth and fluffy—approximately 3-4 minutes.
Once your cakes are cool, assemble them by placing one layer on a cake plate. Spread a luscious layer of frosting over the top. Then, place the second layer on top. Frost the sides and top of the cake generously with the remaining frosting.
Finally, slice, serve, and indulge in the deliciousness of your homemade White Cake!