1 12 oz jar peanut butter (smooth or chunky)
1 16 oz container cake icing (vanilla or chocolate)
Remove the lid and the seal from the peanut butter and heat in the microwave until melted. This will take from 45 to 90 seconds depending on your microwave Stir peanut butter into cake icing. Turn into an 8 or 9 inch pan which has been lined with aluminum foil. Chill in the refrigerator until firm (about an hour). Lift out foil and peel it from the fudge. Cut into squares.
I have tried this with vanilla, chocolate and coconut pecan icings. The first two work very well. The coconut pecan was delicious but never set up enough not to be sticky. Of course, you could eat it and then lick your fingers.