Preheat oven to 350 degrees.
Spray cake pan with baking spray with flour. Set aside.
Mix together cake flour and baking powder in a mixing bowl. Set aside.
Using a stand mixer with the paddle attachment or a hand mixer, beat the butter and sugar until light and creamy. Add egg yolks, one at a time, mixing well.
Drop in lemon rind and mix.
Add milk, alternating with the flour mixture and beat until incorporated.
In a small bowl, beat egg whites until stiff.
Carefully fold the egg whites into the batter until incorporated.
Pour batter into prepared cake pan.
Bake for 20-25 minutes or until toothpick inserted in the center comes out clean.
Remove from cake pan and move to a wire cooling rack.
Cool completely. Once cooled, wrap in plastic wrap and place in the refrigerator.