Roll pastry into an 11 1/2 inch round on a lightly floured board.

Fit the pastry into a 9 inch pie pan; trim and flute the edge.

Preheat oven to 375 degrees (200 C).

In a large bowl, stir together the sugar and melted, cooled butter.

Blend in flour, salt, and grated lemon peel.

Add lemon juice and mix well.

In a small bowl, beat egg yolks to blend.

Stir in milk to the egg yolks.

Stir the egg yolk mixture into the lemon mixture in a medium sized bowl.

In a separate bowl, beat egg whites with an electric mixer until they hold stiff, moist peaks.

Gently fold the beaten egg whites into the lemon mixture.

Pour the lemon filling into the prepared pastry shell.

Bake on the lowest rack of the preheated oven until the filling is richly browned on top and the center feels set when lightly pressed, approximately 45 to 55 minutes.

Let the Lemon Cake Pie cool completely on a rack.

Serve at room temperature.

If made ahead, refrigerate for up to 6 hours.