Whisk together flour, sugar, and salt in a heavy-bottomed saucepan. Add the milk, egg yolks, and butter.
Cook over medium heat whisking constantly until the mixture has come to a bubble and has thickened enough to coat the back of a spoon.
Remove from the heat and stir in the vanilla, pumpkin, and pumpkin pie spice.
Pour filling the prebaked and cooled pie crust, and let cool for about 45 minutes or until room temperature.
Place in the fridge and let it chill completely before adding the whipped cream.