In a mixing bowl, combine pumpkin puree and instant vanilla pudding mix.
Gradually add milk while whisking until smooth.
Stir in pumpkin pie spice until evenly distributed.
Gently fold in the whipped topping until fully incorporated.
Taste and adjust sweetness if needed.
Transfer the pumpkin fluff into a serving bowl.
Cover and refrigerate for at least 2 hours to set.
Before serving, top with crushed graham crackers.
Garnish with pecans or walnuts if desired.