This recipe is from Shirley McNevich's Mom's Best Recipes Vol 1. Published here with her permission.
Don't forget to check Shirley's blog.
(by Aunt Eileen [Knouse] Carter)
1- 18-20oz. jar creamy or crunchy Jif peanut butter
1 container of pre-made frosting (any flavor, any brand)
Put ingredients in a microwave safe bowl. Heat in microwave on high for 3 minutes, or until peanut butter melts. Remove from microwave and stir with a spoon until it's mixed well and smooth. Line an 8 x 8 x 2" pan with foil (you do not need to butter the pan). Pour the fudge into the pan and let it cool at least an hour, and then refrigerate until firm, preferably overnight. Dump upside down on a cutting board, peel off the foil, and cut into squares. Keep refrigerated.