Step 1: Prepare the Pie Crust : Preheat oven to 425°F (220°C). In a medium bowl, mix flour and salt. Cut in butter until mixture resembles coarse crumbs. Gradually add ice water until dough forms. Roll out dough and fit into a 9-inch pie pan. Trim edges. Prick the bottom with a fork, line with parchment, and fill with pie weights. Bake for 12–15 minutes until lightly golden. Remove parchment and weights; bake 3–5 more minutes. Cool completely.

Step 2: Prepare the Lemon Filling : In a medium saucepan, whisk together sugar, flour, cornstarch, and salt. Gradually stir in water, lemon juice, and lemon zest. Cook over medium heat until mixture comes to a boil, stirring constantly. Stir in butter. Slowly whisk about ½ cup hot mixture into egg yolks, then return egg mixture to saucepan. Cook for 2 more minutes, stirring constantly. Pour hot filling into cooled crust.

Step 3: Prepare the Meringue : Preheat oven to 350°F (175°C). In a clean bowl, beat egg whites and cream of tartar until soft peaks form. Gradually add sugar while beating until stiff peaks form. Add vanilla extract and beat briefly. Spread meringue over hot lemon filling, sealing edges to crust to prevent shrinking. Use a spatula to create decorative peaks.

Step 4: Bake the Meringue : Bake for 12–15 minutes until meringue is golden brown. Cool at room temperature for 1 hour, then chill for at least 1 hour before serving.