Preheat your oven to 350°F (175°C).
Grease two 9-inch round cake pans with butter or non-stick spray. Optionally, line the bottoms with parchment paper.
In a medium bowl, whisk together the all-purpose flour, baking powder, and salt.
In a large bowl, cream the unsalted butter and granulated sugar with an electric mixer until light and fluffy, about 3-5 minutes.
Mix in the clear vanilla extract (or almond extract) and lemon zest. Gradually add the beaten egg whites, mixing until well combined.
In a separate bowl, combine the whole milk, sour cream, and neutral oil. Mix until fully combined.
Gradually add the dry ingredients to the butter mixture, alternating with the wet mixture. Begin and end with the dry ingredients. Mix just until incorporated.
Divide the batter evenly between the prepared pans and bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Remove cakes from oven and cool in pans for 10 minutes, then transfer to a cooling rack to cool completely.
Once cool, frost with your favorite frosting, slice, and serve.