In a large mixing bowl, whisk together the pudding mix, brown sugar, and pumpkin pie spice.
Add the half and half and whisk until well combined, and the pudding starts to thicken - about two minutes.
Stir in the pumpkin and vanilla until combined.
Gently fold in the whipped topping to incorporate.
Finally, pour the mixture into the graham cracker crust and gently smooth the top.
Pop in the fridge for at least 3 hours before serving, or ideally overight. **I prefer putting it in the freezer as well, so it slices cleaner.
Top slices with extra whipped topping if desired.
