I found the base for these tasty treats in the 1999 Taste of Home Annual Recipes cookbook, it was titled Chewy Peanut Butter Bars and what really got me was the short ingredient list, these are a super easy one bowl cookie with very basic ingredients you are sure to have on hand. I added Reese's Pieces before baking, and the result was one very tasty treat!
Chewy Reese's Pieces PB Cookie Bars
Put all ingredients except for Reese's Pieces in a big bowl and mix thoroughly with electric mixer, spread into 9 by 13 pan -- you can either spray the pan with cookie spray or line it with aluminum foil and then spray it, so the bars are easy to lift out and evenly cut.
Evenly sprinkle the top of the bars with Reese's Pieces and gently press them down a little bit.
Bake in 350 degree oven for 25 - 35 minutes, I think if you were using a basic 9 by 13 pan 25 minutes would work, but I was using an air bake insulated 9 by 13, which always adds on some extra minutes. Let these cool and set up for a few hours before cutting and serving, do not try to serve them straight from the oven, they really benefit from cooling down.