1. Prepare the Pie Crust: In a medium bowl, combine flour, sugar, and salt. Cut in cold butter using a pastry cutter or fork until pea-sized crumbs form. Gradually mix in cold water, stirring until the dough holds together. Shape into a disk, wrap in plastic, and chill for at least 2 hours (or freeze for 30 minutes).

Preheat oven to 425°F. Roll out the dough to fit a 9-inch pie dish. Press it into the plate and trim the edges. Prick the crust with a fork or use pie weights. Bake for 10-12 minutes until lightly golden. Set aside.

2. Make the Lemon Filling: Whisk sugar, corn starch, water, egg yolks, lemon juice, and zest in a saucepan. Cook over medium to medium-high heat, whisking constantly until thick, like warm pudding (about 10-15 minutes). Remove from heat and stir in butter. Cover to keep warm.

3. Prepare the Meringue: Preheat oven to 375°F. In a small pot, cook water and corn starch over medium heat until thick and clear. Set aside and keep warm.

Beat egg whites with vanilla and salt until soft peaks form. Gradually add sugar while continuing to beat until the mixture forms stiff, glossy peaks. Then, slowly incorporate the warm corn starch mixture, beating until fully blended and the meringue is light and fluffy.

4. Assemble the Pie: Pour the hot filling into the baked crust. Spread meringue over the hot filling, sealing all the way to the edges. Bake at 375°F until meringue is lightly golden, about 8-10 minutes.

Cool on a wire rack for 1-2 hours, then chill in the fridge for 5-6 hours or overnight before slicing.