01 - Set oven to 400°F and allow it to fully preheat.
02 - Fit the unbaked pie crust into a 9-inch pie pan and crimp the edges as preferred.
03 - Pour 1 1/2 cups water directly into the prepared pie crust.
04 - In a mixing bowl, blend the granulated sugar and all-purpose flour until well incorporated. Sprinkle evenly over the water.
05 - Drizzle vanilla extract across the filling and sprinkle with a pinch of salt.
06 - Slice butter into thin pieces; arrange evenly over the surface of the filling.
07 - Place pie pan on the lower oven rack and bake at 400°F for 30 minutes.
08 - Reduce oven temperature to 375°F and bake an additional 20 minutes, or until the crust is golden and filling is softly set.
09 - Remove pie from oven; cool completely at room temperature, then refrigerate at least 2 hours before slicing.