In a medium saucepan over low to medium-low heat, combine large marshmallows, pure pumpkin, cinnamon, pumpkin pie spice, and a pinch of salt. Stir frequently until everything melts down into a smooth, creamy mixture, about 10 minutes.

Once melted, remove from heat and transfer to a large mixing bowl. Allow it to cool to room temperature for approximately 30 minutes, stirring occasionally.

When the mixture has cooled completely, gently fold in the thawed Cool Whip using a spatula.

Carefully pour the creamy filling into the store-bought graham cracker crust, smoothing it out with a spatula.

Cover the pie with its lid or plastic wrap and refrigerate for at least 8 hours, or preferably overnight.

After chilling, slice into generous portions and serve chilled, topped with whipped cream if desired.