Add the softened cream cheese, peanut butter, and powdered sugar to a large mixing bowl. Beat together until the mixture is smooth and fully combined.
Add the Cool Whip to the bowl and gently stir until the filling becomes light, fluffy, and evenly blended.
Transfer the peanut butter filling into the prepared graham cracker crust and spread it out into an even layer.
Place the pie in the refrigerator and chill for at least 4 hours, or until the filling has firmed up.
Slice the pie and serve with extra Cool Whip and chopped Reese’s Cup minis on top if desired.