Mix sugar, butter, flour, lemon juice and rind, milk salt and egg yolks in large bowl. Stir with a whisk until yolks are thoroughly mixed. (Mixture will look curdled but that's normal.) Beat egg whites until stiff but not dry and fold into lemon mixture.
Bake crust at 425 degrees for 10 minutes. Remove from oven and cool slightly. Pour lemon mixture into piepan and bake in preheated oven at 350 degrees for about 40 minutes or until top bounces back when touched with your finger. Cool completely before cutting. Store leftovers in refrigerator.
Can also be baked without the crust in a piepan or individual custard cups. Pour lemon mix in them, set in a pan. Pour in hot water to go 1 inch up the sides and bake in preheated 350 degree oven for about 20-30 minutes until done as per test for pie.