FOR THE CRUST
1 1/4 cups all-purpose flour (spooned and leveled), plus more for dusting
1/3 cup sugar
1/4 teaspoon salt
8 tablespoons (1 stick) cold unsalted butter, cut into small pieces
FOR THE FILLING
6 cups (six 1/2-pint containers) fresh blueberries, rinsed and dried
2 tablespoons cornstarch
2 teaspoons finely grated lemon zest
3 tablespoon fresh lemon juice
2/3 cup sugar
Pinch of salt
Preheat oven to 375 degrees. In a food processor, combine flour, sugar, salt, and butter; process until large moist crumbs form (dough should hold together when squeezed).
Transfer dough to a 9-inch round tart pan with a removable bottom; with floured fingers, press evenly into bottom and up sides. Freeze until firm, about 15 minutes; prick bottom of dough all over with a fork. Bake until golden, 20 to 25 minutes; cool completely.
Meanwhile, reserve 1 cup of the prettiest berries for topping. In a medium saucepan, bring 1/4 cup water and 1 1/2 cups berries to a boil over high heat. Reduce heat; simmer, stirring occasionally, until berries begin to break down, 3 to 4 minutes.
In a small bowl, mix cornstarch with 2 tablespoons water; stir into berries in pan. Add lemon zest and juice, sugar, and salt. Bring to a boil; reduce heat. Simmer, stirring, just until mixture begins to thicken, 30 to 60 seconds. Remove from heat.
Stir in remaining 3 1/2 cups fresh berries. Immediately pour hot berry mixture into cooled tart shell, and smooth with a spatula.
Scatter reserved berries on top, pressing down lightly to help them adhere. Refrigerate until cool, about 30 minutes and up to overnight.