Preheat oven to 350�F.
In a bowl, combine flour, baking powder, and salt. Sift several times so that dry ingredients are very fine.
In a separate bowl, use and electric mixer to beat egg whites until forming soft peaks. Gradually beat in 1/2 cup of sugar until stiff peaks form; set aside.
In a clean bowl, cream butter with an electric mixer until pale and fluffy. Mix in remaining sugar, egg yolks, almond extract, and lemon zest until well combined.
Fold in sifted flour mixture and then egg whites until everything is just combined and fluffy.
Pour into a heavily greased cake pan and bake for 45 minutes until an inserted knife comes out clean.