In a bowl, whisk together flour, salt, and sugar. Cut in cold butter until coarse crumbs form. Add ice water, 1 tablespoon at a time, until dough comes together. Shape into a disc, wrap, and refrigerate for at least 1 hour.
Preheat oven to 375°F. Roll dough to a 12-inch circle and fit into a pie dish. Trim and crimp edges. Line with parchment, fill with pie weights, and bake for 20 minutes. Remove weights and bake 8-10 minutes more until golden. Cool completely.
In a saucepan, combine cranberries, 1 cup sugar, water, lemon zest, and juice. Bring to a boil, stirring occasionally. Boil for 8-10 minutes until cranberries pop and soften and liquid turns deep red.
Strain the hot cranberry mixture through a fine mesh sieve, pressing on solids to extract about 2 cups of liquid. Discard solids. Whisk cornstarch with 2 tablespoons cold water until smooth. Whisk in egg yolks, then stir in strained liquid. Cook over medium heat, stirring constantly, until mixture boils and thickens, about 3-5 minutes. Remove from heat and stir in cold butter and salt until smooth.
Pour the warm cranberry lemon filling into the cooled crust and spread evenly. Keep filling warm while preparing the meringue.
In a clean, grease-free bowl, beat egg whites and cream of tartar on medium speed until foamy. Gradually add sugar, a tablespoon at a time, beating until glossy and stiff peaks form, about 5-7 minutes. Beat in vanilla and salt during the last 30 seconds.
Preheat oven to 350°F. Spoon meringue over warm filling, sealing against the crust edges. Swirl into decorative peaks. Bake for 12-15 minutes until golden, or use a kitchen torch to brown.
Let pie cool on a wire rack for 1 hour, then refrigerate for at least 3 hours until filling is fully set before slicing. Use a sharp knife dipped in hot water and wiped clean for neat slices.