Mix the frosting with the peanut butter as best you can in a 8×6 (approximate size) microwavable safe dish. Microwave 1 minute, stop and stir. If melts together and blends easily, just mix with fork and refrigerate. If not, stick back in microwave another minute. Mix well with fork, and put in refrigerator. After 1-2 hours, the fudge should be cooled and ready to cut and enjoy. Delicious.
If you like fudge with nuts, you will want to use the crunchy peanut butter.