In a bowl, combine graham cracker crumbs, sugar, and melted butter. Press into the bottom of a 9x13 inch pan.
In a large bowl, cream together peanut butter and softened butter until smooth. Gradually beat in powdered sugar, then add milk and vanilla extract. Mix well.
Spread the peanut butter filling over the graham cracker crust. Refrigerate for at least 2 hours before serving.
Cut into bars and enjoy!
Notes
For a chocolate topping, melt chocolate chips with a tablespoon of butter and spread over the chilled bars. Return to the refrigerator to set.