Line a 13 x 9 pan with wax paper and coat with spray or margarine.
In Dutch oven over medium heat melt butter,sugar and evaporated milk. Bring to a boil and constantly stir for 5 minutes. Remove from heat.
Sir in Peanut butter, marshmallow cream and vanilla until thoroughly blended.
Pour evenly into prepared pan and cool in the refrigerator until firm. (about 2 hours)
Cut into 1 " sq and store in airtight container. Makes about 50 squares.