Beat together shortening and 1½ c. sugar. Blend in vanilla, lemon juice and peel. Add egg yolks, one at a time, blending just until smooth after each addition.
Sift together flour, baking powder, soda and salt. Add alternately with buttermilk to first mixture, blending until smooth.
Beat egg whites until frothy, then gradually beat in remaining ¾ c. sug