To make the crust add the graham cracker crumbs and sugar to a large mixing bowl and stir to combine. Then add the melted butter and stir until crumbly.
Firmly press the crust mixture into a 9-inch pie plate.
Refrigerate the crust while you make the filling.
For the filling, whisk the sugar, cornstarch, and pumpkin pie spice in a saucepan until combined.
Stir in the milk, and heat over medium heat, stirring continuously, until the mixture thickens, and begins bubbling.
Whisk in the vanilla extract and pumpkin until combined.
Pour filling into pie crust, and refrigerate for at least 3 hours. (For a firmer pie filling refrigerate overnight.)
To make whipped topping beat together a cup of cream and powdered sugar until stiff peaks form. Spread it over the top of the pie before serving.
For an optional finishing touch you can sprinkle a bit of cinnamon over it.