Spray a 9x9inch square dish, and set aside. Combine the sugar and milk in a 3 quart heavy pot. Stir to mix well and place over moderate heat.
Bring to a boil, stirring until the sugar dissolves, then cover and let boil for 2-3 minutes. Uncover and wash down the sides of the pot with a pastry brush dipped in cold water.
Continue to boil over medium heat, without stirring, to the soft ball stage (234F). Remove from the heat and stir in the marshmallow cream, peanut butter and vanilla. Mix well and spread in the spray dish. Cool and cut into squares. Store in airtight container.