In a medium saucepan, mix sugar, cornstarch, flour and salt. Steadily stir in water.
Cook dinner and stir over medium warmth till thickened and bubbly.
Scale back warmth; cook dinner and stir 2 minutes extra. Take away from the warmth.
Steadily stir 1 cup of scorching combination into egg yolks; return all to saucepan. Deliver to boil.
Cook dinner and stir for two minutes. Take away from the warmth. Stir within the butter, lemon juice and zest till easy. Pour into pastry shell. In a bowl, beat egg whites and salt till stiff however not dry peaks are fashioned.
Steadily beat in sugar till comfortable peaks kind.
Unfold over pie, sealing edges to pastry.
Bake at 350° for 12-Quarter-hour or till meringue is golden.