In a food processor, combine graham crackers, sugar, and butter. Pulse until blended well.
Press the mixture onto the bottom and up the sides of a 9-inch plate and bake for 15 minutes, cool.
Clean out the food processor and combine the cream cheese, peanut butter, and powdered sugar. Process until almost smooth.
Gently fold in the whipped cream and pour into the pie shell.
Chill for 6-8 hours.
Make the fudge topping:
Combine 2/3 cup whipping cream, 1/3 cup sugar and 4 oz semi sweet chocolate in a sauce pan and simmer over low heat. Whisk together and cook until thickened.
Remove from heat and add vanilla. Whisk until smooth. Let cool.
Top cooled peanut butter pie with cooled fudge sauce.
Let the pie set up again with the fudge sauce on top for another 4-6 hours.
-You may also make this with Oreos in stead of chocolate graham crackers. If using Oreos, crush the cookies (use about 3/4 of a package), and 1/3 cup of melted butter. No need to bake the crust. Press into pie plate and proceed as directed.