Preheat oven to 450° F.
In a large bowl cream butter and sugar. Add flour and salt. Incorporate completely. Add beaten egg yolks. Mix well. Add lemon rind, and lemon juice. Mix well. Whisk in milk.
In a medium glass or metal bowl, beat egg whites until soft peaks form. Fold into mixture. Pour mixture into pastry shell.
Bake at 450° F. for 10 minutes lower the heat to 325° F. and bake for 25
to 35 minutes or until golden brown and firm in center.