Mix cake mix, peanut butter, eggs and oil in a bowl well until combined and no powder is showing. Preheat oven to 350 degrees now.
Fold in chocolate chips/peanut butter chips and if you choose to add crushed peanuts fold them in too.
Spray an 8x8 pan with non stick spray or line with parchment paper.
Spoon batter into pan and spread out so it is an even thickness across the pan so it cooks evenly.
Place into the middle rack of your oven for about 25 minutes or until the edges are a light brown. (if you're a bit at altitude you might need 30 min. until edges are golden brown)
You DO NOT want to overcook these, you want slightly crispy on edges but very soft in the middle. It is important to take out at this point, leave in the pan and allow them to cool on a cooling rack to firm up before slicing.