Cream butter and sugar together.
Add egg yolks and beat well.
Add flour, salt, lemon juice and rind; mix thoroughly.
Add buttermilk and mix well.
Fold in beaten egg whites.
Pour filling into crust and bake for 10 minutes at 450 degrees.
Lower heat to 350 degrees and continue baking 40 minutes.
May need to cover crust edges with foil it starts to get too brown.
