In a mixing bowl, combine flour and butter for the crust. Add ice water and mix until dough forms. Press into a pie dish and bake for 15 minutes.
In a saucepan, combine sugar, flour, cornstarch, and salt for the filling. Gradually stir in water, cooking over medium heat until thickened. Remove from heat and stir in butter, egg yolks, lemon juice, and zest. Return to heat and cook for 2 more minutes. Pour into baked crust.
In a mixing bowl, beat egg whites until foamy. Gradually add sugar and continue to beat until stiff peaks form. Spread meringue over hot filling, sealing edges to crust.
Bake in preheated oven for 10 minutes, or until meringue is golden brown. Cool before serving.
Notes:
Ensure the meringue is spread to the edges to prevent shrinking.