Break apart the candy bars and add to a large microwave safe bowl.
Add butter to chocolate bar pieces.
Microwave for 90 seconds. Stir and continue to microwave for 30 seconds.
Once the chocolate and butter have melted, stir in the vanilla extract.
Fold in 1/2 Cool Whip until it's well combined. Add the remainder of Cool Whip.
Spoon into pie crust and refrigerate for at least two hours before serving.