Line 8 x 8 inch pan with parchment paper, allowing a 2 inch overhang on all sides. Lightly spray the parchment with non-stick cooking spray. Set aside.
Bring sugar, milk, and butter to a boil over medium heat. Cook until the mixture reaches the soft ball stage or 240º F on a candy thermometer. Remove from heat and stir in vanilla, peanut butter and marshmallow cream. Mix until smooth. Pour into prepared pan and allow to cool completely.
To cut the fudge, lift the fudge out of the baking pan using the overhanging parchment edges. Cut into 1-inch squares. Store fudge in an airtight container in the refrigerator.