1. Preheat oven to 425°F (220°C).
2. For the crust: In a bowl, mix flour and butter until crumbly. Add ice water and mix until dough forms. Roll out and place in pie dish. Bake for 10-12 minutes.
3. For the filling: In a saucepan, combine sugar, cornstarch, and salt. Gradually stir in water, lemon juice, and zest. Cook over medium heat, stirring constantly, until mixture thickens and boils. Stir in butter. Gradually stir in egg yolks, cook for 2 more minutes. Pour into baked crust.
4. For the meringue: In a bowl, beat egg whites and cream of tartar until soft peaks form. Gradually add sugar, beating until stiff peaks form. Spread meringue over hot filling, sealing edges to crust.
5. Bake in preheated oven for 10 minutes, or until meringue is golden brown. Cool before serving.