Measure peanut butter chips into one bowl and chocolate chips into another; set aside.
Butter 8-inch square pan; set aside.
Combine sugar, marshmallow creme, evaporated milk and butter in heavy 3-quart saucepan.
Cook over medium heat, stirring constantly, until mixture boils; continue cooking and stirring for 5 minutes.
Remove from heat; stir in vanilla.
Immediately stir half the hot mixture into peanut butter chips until completely melted.
Quickly pour into prepared pan.
Stir remaining hot mixture into chocolate chips until completely melted.
Quickly spread over top of peanut butter layer; cool until set.
Cut into 1-inch squares.
Store in airtight container in cool, dry place.