In a microwave safe bowl, combine the peanut butter chips and sweetened condensed milk. Microwave on high for 20 second increments stirring in between until chips are completely melted and mixture is smooth and creamy. This will take anywhere from 1 to 1½ minutes.
Stir in the creamy peanut butter and vanilla extract and then gently add the marshmallow creme, stirring only until incorporated. If adding mini marshmallows, fold them in at this time.
Transfer to a parchment lined (or well greased) 8×8 inch pan. Spread into one even layer. Chill until set.
Cut into 1 to 1½ inch pieces and store in an airtight container. If kept in the refrigerator, this fudge can keep for about 2 weeks.
