01 - Set oven to 400°F (200°C) and allow to preheat fully.
02 - Fit the unbaked pie crust into a 9-inch pie pan, crimping edges as preferred.
03 - Pour 1 1/2 cups water directly into the pie crust.
04 - Mix granulated sugar and all-purpose flour in a bowl until uniformly blended. Sprinkle evenly over the water inside the crust.
05 - Drizzle vanilla extract over the filling and add a pinch of salt.
06 - Slice unsalted butter into thin pats and arrange evenly on top of the filling.
07 - Place pie on the lower oven rack and bake for 30 minutes at 400°F (200°C).
08 - Reduce oven temperature to 375°F (190°C) and bake an additional 20 minutes until crust is crisp and the filling is gently set but still jiggles slightly in the center.
09 - Remove from the oven and cool completely to room temperature. Refrigerate for at least 2 hours to achieve a creamy texture before slicing.