Butter a baking pan and set aside until needed. Put milk and sugar in to a medium saucepan. Stir the mixture until blended well. Bring the mixture to a boil over medium heat. Boil the mixture for 3 minutes. Remove the mixture from the heat. Turn the stove off. Add marshmallow crème and peanut butter to the mixture. Stir the mixture until blended well. Pour the mixture evenly in to the prepared pan. Allow the fudge to cool completely and serve.