Preheat oven to 375° F. Line a 8 by 8-inch or 9 by 9-inch pan with foil and spray with cooking spray (Do not skip this step, do not use wax or parchment paper).
Line the pan with one flat layer of graham crackers. You will need to break the graham crackers to fill in odd-shaped places (or slice the graham crackers on a cutting board with a knife for ultra-precision). Sprinkle the marshmallows over the graham cracker layer and bake for 6 to 7 minutes, or until marshmallows have begun to puff up or are showing first signs of browning. Remove from the oven and sprinkle white chocolate chips over the top and bake for 2 minutes more and remove from the oven and allow pan to cool a bit.
Make the Peanut Butter Cocoa Krispies Layer by placing chocolate chips, peanut butter, and butter in a microwave-safe bowl and heating for 45 to 60 seconds, then removing and stirring. Microwave again for 30 more seconds, or until mixture has fully melted. Stir until completely melted and smooth. Add the vanilla extract and Cocoa Krispies and stir to coat. Pour this mixture over the top of the melted marshmallow and white chocolate chip layer.
Place the pan in the freezer for 20 minutes or in the refrigerator for at least one hour to set up completely before slicing and serving. Store the bars in an airtight container on the countertop, or freeze for up to 3 months for longer-term storage, knowing that the crackers may not be as crunchy if frozen for long periods.