Lightly grease a 9-inch square pan with cooking spray. Set aside.
For the peanut butter layer: in a large bowl, beat together butter, brown sugar, powdered sugar, peanut butter, and graham cracker crumbs until well-combined (it may still be a bit crumbly). Press the peanut butter layer into the pan as evenly as possible.
For the chocolate layer: Boil water in a medium saucepan. When the water is boiling, place a heatproof bowl on top. Add the chocolate chips and butter and melt, stirring frequently. Remove the bowl from the heat and evenly spread it on top of the peanut butter layer. Top with peanuts. Cover with plastic wrap (don't let it touch the chocolate layer. Use toothpicks if necessary) and refrigerate until firm, about 1 hour. Cut into squares before serving.
Recipe by Chocolate Moosey at http://www.chocolatemoosey.com/2012/07/22/chocolate-peanut-butter-squares-for-sundaysupper/