Prepare two baking sheets by lining them with wax paper. Place the old fashioned oats and creamy peanut butter into a large mixing bowl and set aside. In a medium saucepan set over medium heat, blend together the granulated sugar, milk, butter, and cocoa powder, stirring continuously until the mixture reaches a vigorous boil. Maintain this boil for exactly one minute while stirring without pause, then incorporate the vanilla extract. Remove the pan from the heat source and promptly pour the hot mixture over the oats and peanut butter. Stir thoroughly until the ingredients are evenly combined. Using a large spoon, drop generous spoonfuls of the cookie mixture onto the prepared wax paper. Allow the cookies to cool entirely. Enjoy immediately or store in an airtight container for up to one week.