In a bowl cream butter, short and 1 c sugar. Add lemon peel and vanilla; mix well. Comb flour, bkg pwd and salt. Grad add to creamed mix alt with milk, mixg well after each addition; set aside. Beat egg whites til soft peaks form. Grad add rem sugar, beatg til stiff peaks form. Fold into the cream mix. Pour into 3 greased and waxed paper lined 23 cm round cake pans. Bake at 180ºC or 15-20 min or til cake test done. Cool in pans 10 min before rem to a wire rack. For filling, comb sugar and flour in a saucepan. Grad add milk; cook and stir til thickened and bubbly. Cook and stir 2 min more. Rem from heat. Grad stir a little of hot fillg into the yolks; return all to the pan. Bring to a gentle boil. Cook and stir 2 min more. Remove from heat and stir in lemon juice, vanilla and peel. Cover and cool. Fold in the cream then spread between each layer and on top of cake. Cover and chill.