Make sure your kitchen table is cleared off. Pull and cut a long strip, or 2, of wax paper, and lay it out on table.
Use a double-boiler type system where you have 2 deep pots of equal size, so you can stack one on top of the other. Fill bottom pot half-full of water, and bring to a medium boil (you will probably need to adjust temperature according to type of stove used). Stack empty pot on top of it.
Put the peanut butter, margerine, and marshmallow cream into top pot.
As soon as the ingredients start to melt, start stirring them together until they are well blended, smooth and creamy.
Gradually stir in flour until well blended.
Add Karo Syrup, and vanilla until well blended.
Boil for 15 minutes. Reduce heat to low/simmer.
Gradually add cereal until well blended. Turn off stove.
Carefully remove HOT water pot, and set in sink. Run cold water into HOT water until water is cool enough to pour out.
Quickly spoon cookie mixture onto wax paper in size of cookies desired. Let cool for 1 hour. Enjoy !