01 - Combine flour and salt in a bowl. Cut in cold butter until mixture resembles coarse crumbs. Gradually add ice water, stirring until dough forms. Shape into disk, wrap, and chill 30 minutes. Roll out dough and fit into 9-inch pie dish. Trim edges, line with parchment and fill with weights. Bake at 400°F for 15 minutes, remove weights, then bake 10 more minutes. Cool.
02 - Whisk sugar, cornstarch, and salt in saucepan. Gradually add water, lemon juice, and zest. Cook over medium heat, stirring constantly until thick and bubbling. Temper egg yolks with a spoonful of hot mixture, then return to saucepan and cook 2 minutes more. Remove from heat, stir in butter, then pour into cooled crust.
03 - Beat egg whites and cream of tartar until soft peaks form. Gradually add sugar while beating until stiff and glossy. Mix in vanilla extract. Spread meringue over hot filling, sealing edges to crust.
04 - Bake at 350°F for 15 to 18 minutes until meringue is golden. Cool at room temperature, then chill for at least 1 hour before serving.