Preheat oven to 350°F (175°C).
In a mixing bowl, combine flour, sugar, and salt. Cut in butter until mixture resembles coarse crumbs. Stir in egg yolk and water until dough forms. Press into a tart pan.
Bake crust for 15 minutes. Let cool.
In a saucepan, combine sugar, cornstarch, and salt. Gradually stir in water, lemon juice, and zest. Cook over medium heat until thickened. Remove from heat and stir in butter and egg yolks. Pour into crust.
In a mixing bowl, beat egg whites and cream of tartar until soft peaks form. Gradually add sugar, beating until stiff peaks form. Spread over lemon filling.
Bake for 10 minutes, or until meringue is golden brown. Cool before serving.