Preheat the oven to 350F. Unroll the unbaked 9-inch pie crust into a pie dish and crimp the edges neatly.
In a small bowl, whisk the cornstarch and water together vigorously until you have a smooth slurry.
In a large mixing bowl, combine the dark corn syrup, brown sugar and melted butter. Whisk until the sugar begins to dissolve.
Make sure the melted butter is not too hot before adding it, so the ingredients mix together smoothly into a rich base. Pour the cornstarch slurry and the vanilla extract into the syrup mixture, whisking well to combine everything into a cohesive liquid.
Stir the pecan halves into the bowl, ensuring all the nuts are completely coated in the sweet syrup.
Pour the entire pecan filling into your prepared pie crust, using a spatula to spread the nuts into an even layer.
Bake the pie for 45 to 55 minutes, until the edges are set and the center has just a slight jiggle to it.
Remove the pie from the oven and let it cool completely on a wire rack for at least three hours before slicing to allow the filling to set.
