Preheat your oven to 350°F (175°C) and prepare a 9x9 inch baking pan with parchment paper.
In a medium bowl, whisk together the cake flour, baking powder, baking soda, and salt.
In a large bowl, cream together the butter and granulated sugar until light and fluffy.
Mix in the egg whites, vanilla extract, and lemon zest until smooth.
Gradually add the dry ingredients and buttermilk to the wet ingredients, mixing until combined.
Pour the batter into the prepared pan and bake for 36-42 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake cool in the pan for 30 minutes before transferring to a wire rack to cool completely.