In a food processor, all ingredients for crust (flour, butter, sugar, salt). Process until large crumbs form (dough should hold together when squeezed.
Transfer dough mixture into a 9" round tart pan with removable bottom.
With floured hands, press dough evenly into bottom and sides. (Or use a floured 1 cup measure as per instructions in the video here).
Place crust in freezer until firm, approx 15mins.
Prick bottom of crust all over with a fork.
Bake until golden, 20 to 25 minutes; cool completely.
Filling:
Reserve 1 cup of blueberries for the topping.
In a medium saucepan over high heat, bring 1/4 cup water and 1 1/2 cups blueberries to a boil. Reduce heat and simmer, stirring occasionally, for 3-4 minutes until berries begin to break down.
In a small measuring cup combine cornstarch and 2 Tbsp water to form a slurry.
Stir slurry into berries. Add lemon zest & juice, sugar, and salt and bring to a boil.
Reduce heat and simmer until mixture thickens (30-60 secs).
Remove from heat, stir in 3 1/2 cups blueberries
Immediately pour hot berry mixture into cooled tart shell and smooth with a spatula.
Top with reserved 1 cup blueberries, pressing down lightly to help them adhere.
Top with strips of lemon zest.
Refrigerate until cool, about 30 minutes and up to overnight.