Make the Pie Crust:

1. Prepare the dough: In a large bowl, whisk together flour, salt, and sugar. Add cold butter cubes and use a pastry cutter or fork to cut the butter into the flour until the mixture resembles coarse crumbs with pea-sized butter pieces remaining.
2. Add water: Drizzle in ice water one tablespoon at a time, tossing with a fork after each addition. Add just enough water until the dough begins to come together when pressed. It should not be wet or sticky.
3. Chill: Shape dough into a disk, wrap tightly in plastic wrap, and refrigerate for at least 30 minutes (or up to 2 days).
4. Roll out: On a lightly floured surface, roll the dough into a 12-inch circle about ⅛-inch thick. Carefully transfer to a 9-inch pie dish, pressing gently into the bottom and sides. Trim excess dough, leaving a 1-inch overhang, then fold under and crimp the edges decoratively.
5. Blind bake: Preheat oven to 375°F. Prick the bottom of the crust with a fork, line with parchment paper, and fill with pie weights or dried beans. Bake for 15 minutes, then remove weights and parchment. Bake for another 10-12 minutes until golden. Let cool while preparing filling.

Make the Lemon Filling:

6. Combine dry ingredients: In a medium saucepan, whisk together sugar, cornstarch, and salt until no lumps remain.
7. Add liquids: Gradually whisk in water until smooth. Place over medium heat and cook, whisking constantly, until mixture comes to a boil and thickens significantly, about 8-10 minutes.
8. Temper egg yolks: In a separate bowl, whisk egg yolks. Slowly pour about 1 cup of the hot sugar mixture into the yolks while whisking constantly (this prevents scrambling). Pour the yolk mixture back into the saucepan.
9. Finish filling: Return to medium heat and cook, whisking constantly, for 2 more minutes until very thick. Remove from heat and whisk in lemon juice, lemon zest, and butter until smooth and glossy.
10. Strain and pour: Pour filling through a fine-mesh strainer into the baked pie crust. Smooth the top with a spatula. Press plastic wrap directly onto the surface to prevent a skin from forming while you make the meringue.

Make the Meringue:

11. Preheat oven: Increase oven temperature to 350°F.
12. Whip egg whites: In a completely clean bowl of a stand mixer (or using a hand mixer), beat egg whites and cream of tartar on medium speed until soft peaks form, about 2-3 minutes.
13. Add sugar gradually: With mixer running, gradually add sugar one tablespoon at a time, beating well after each addition. Once all sugar is incorporated, increase speed to high and beat until stiff, glossy peaks form and sugar is completely dissolved (about 5-7 minutes total). Test by rubbing meringue between your fingers—it should feel completely smooth. Beat in vanilla extract.
14. Top the pie: Remove plastic wrap from lemon filling. Immediately spoon meringue over the hot filling, starting at the edges and working toward the center. Make sure meringue touches the crust all around (this prevents shrinking). Use the back of a spoon or offset spatula to create decorative peaks and swirls.
15. Bake: Bake for 12-15 minutes until meringue is golden brown on the peaks. Watch carefully to prevent burning.
16. Cool properly: Remove from oven and let cool on a wire rack at room temperature for 1 hour, then refrigerate for at least 3-4 hours before slicing. This cooling process is crucial for clean slices!