Preheat your oven to 350°F (175°C). Grease and flour three 9-inch round cake pans.
In a medium bowl, combine the flour, baking powder, and salt. Whisk together until well mixed.
In a large mixing bowl, cream the softened butter and granulated sugar together until light and fluffy. This should take about 4-5 minutes.
Add the egg whites and vanilla extract to the butter mixture, mixing until fully incorporated.
Gradually add the dry ingredients to the wet mixture, alternating with the whole milk. Start and end with the dry ingredients, mixing just until combined. Be careful not to overmix.
Divide the batter evenly among the prepared cake pans. Smooth the tops with a spatula.
Bake in the preheated oven for 25-30 minutes or until a toothpick inserted into the center comes out clean.
Once baked, allow the cakes to cool in the pans for about 10 minutes. Then, carefully remove the cakes from the pans and transfer them to wire racks to cool completely.
Once the cakes are completely cooled, frost with your favorite frosting. A simple buttercream or cream cheese frosting works beautifully!