Once the pre-baked pie has cooled to room temperature completely, center a rack in the oven and preheat to 350 (F). Set the pre-baked pie crust on a baking sheet.
In a medium, heavy bottomed saucepan, whisk together 1 cup granulated sugar, 1 tablespoon cornstarch, and 1/4 teaspoon kosher salt until combined. Whisk in 6 large eggs until incorporated. Add 2/3 cup passionfruit puree and whisk until the mixture is a homogenous, sunny yellow.
Fit a candy thermometer to the side of the pan and place the pan over medium heat. Cook the mixture, whisking constantly to prevent it from curdling, until the mixture thickens up, lightens in color, and registers 160 (F) on the candy thermometer; this should take around 10 minutes. Remove the pan from the heat and add 1/2 cup unsalted butter one cube at a time, whisking until the mixture is smooth and all the butter has fully incorporated. Whisk in 1/2 teaspoon pure vanilla extract.
Pour the passionfruit curd into the pre-baked pie shell and bake in the preheated oven for 20 to 25 minutes, until the edges of the filling have puffed but the center is barely set. You can test this by giving the baking sheet a jolt in the oven — the center should still wobble slightly when you pull it out. If it's pretty solid, you've overcooked it!
When the pie has finished baking, transfer to a wire rack to cool completely to room temperature, before chilling in the refrigerator overnight before slicing and serving with the crème fraîche whipped cream.