This is a classic school lunch recipe. Lately, my sisters and I have been having a hard time finding the puff rice. The only kind we can find comes in bags (not boxes) in the cereal section.
3 cups Karo syrup
3 cups sugar
Microwave this mixture on high for 3 minutes. Stir up, then microwave for 3 minutes more.
Add 3 cups peanut butter and mix well.
Pour over a big bowl of puffed rice and stir to coat. I use one of those huge Tupperware bowls and start out with less puff rice than I think I'll need. I gradually add more and stir until it is all well coated, but not too sticky. Press the soft mixture into a large cookie sheet. Cut into squares to serve.