Add the thawed whipped topping to the bowl. Gently fold it into the peanut butter mixture using a spatula, turning the bowl as you go, until the filling is smooth, light, and uniform in color. Try not to overmix so the filling stays airy.
Spoon the peanut butter filling into the graham cracker crust, spreading it out evenly with the back of a spoon or an offset spatula. Smooth the top so it looks neat and creamy.
Refrigerate the pie for at least 2 hours, or until the filling is firm enough to slice cleanly. For the best texture and flavor, you can make it earlier in the day and chill until Sunday dinner.
When ready to serve, slice the pie into 8 wedges using a sharp knife. Wipe the knife clean between cuts for the neatest slices, then serve directly from the glass pie plate.
If you want to dress this up without adding extra stress, sprinkle the top with crushed graham crackers or a handful of chopped roasted peanuts before chilling. For a chocolate twist, drizzle a little chocolate syrup over each slice right before serving or use a chocolate graham crust instead of plain. You can also swap in chunky peanut butter if you like a bit of texture in the filling, just know it won’t be quite as smooth. For make-ahead prep, assemble the pie the night before and cover it tightly with plastic wrap; it actually slices even better the next day. If you’re feeding a crowd, double the recipe and divide the filling between two crusts—no extra effort, just twice the payoff. And if you need it slightly less sweet, reduce the powdered sugar to 3/4 cup and taste as you go until it hits your perfect balance.