1Line 13x9x2 inch pan with foil. In large heatproof bowl place 3 cups peanut butter chips; set aside. In second large heatproof bowl place remaining 1 cup peanut butter chips and the chocolate chips; set aside.
2In heavy 5 quart saucepan place sugar, marshmallow creme, evaporated milk and butter. Cook over medium heat stirring constantly until mixture comes to a full rolling boil; boil and stir for 7 minutes. Remove from heat and stir in vanilla.
3Immediately add half of hot mixture to each of reserved bowls. Beat peanut butter mixture until chips are completely melted; immediately spread in prepared pan.
4Beat chocolate-peanut butter mixture until chips are completely melted; immediately spread over the peanut butter layer.
5Refrigerate until firm. Remove from pan; peel off foil and cut into squares. Store in airtight container.