This was the favorite custard pie of the late President Coolidge.
Beat egg yolks until thick and lemon colored. Add lemon juice and rind, sugar, salt, flour, butter, and milk. Fold in egg whites, beaten stiff. Pour into unbaked pastry shell (with edges fluted) and bake in hot oven (450 degrees F) 10 minutes; reduce heat to moderate (350 degrees F) and bake 20 minutes longer.