Combine sugar, butter and milk in a large, heavy pot. Bring to a boil stirring constantly. Be very careful not to burn!!! Cook until mixture forms a firm ball when tested in cold water. About 15 minutes of boiling. Remove from heat and add the marshmallow cream and the peanut butter and mix thoroughly. Turn into a 9x12 buttered pan and allow to partially set. Cut into serving size pieces and allow to fully set. This is the original recipe. Adding an extra jar of peanut butter still makes an excellent fudge which is more peanut buttery and less sweet.