Preheat oven to 350 degrees.
Combine ½ cup sugar with flour and sift together 4 times. Set aside.
Beat egg whites (enough raw egg whites to fill 1 ½ cups), salt and cream of tartar on high speed until eggs make medium firm peaks, approximately, 1 minute.
Continue mixing at medium speed while adding remaining 1-1/2 cups of sugar, by sprinkling sugar over egg whites while mixing.
Beat until thick and shiny.
Add vanilla and lemon zest and continue beating until very thick (about 1 minute).
Fold ¼ of the sifted flour mixture into the egg whites using a spatula.
Continue folding in the flour mixture until all is incorporated.
Bake in 10" tube pan 35-40 minutes.
Invert pan to cool completely before removing cake from pan.