Preheat your oven to 350°F (175°C) and grease two 9-inch round cake pans.
In a medium bowl, whisk together flour, baking powder, and salt.
In a large bowl, cream the butter and sugar until light and fluffy.
Add egg whites and vanilla extract to the butter mixture, mixing until well incorporated.
Gradually add the dry ingredients to the wet ingredients, alternating with milk.
Mix until just combined, being careful not to overmix.
Divide the batter evenly between the prepared pans.
Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.
Allow cakes to cool in pans for 10 minutes, then transfer to a wire rack to cool completely.
Frost with your favorite frosting and decorate as desired.