Prepare a 9”x13” baking dish (glass or metal) by lightly spraying with cooking spray (or rub pan with a bit of butter).
Prep (chop & measure) all dry ingredients, then add cereal, oreos, pretzels and chips to a large bowl.
In a separate large (microwave safe) bowl, add the marshmallows and butter (chop into a few pieces).
Microwave the butter and marshmallows 2-3 minutes until the marshmallows are super fluffy and melty.
Spray a rubber spatula slightly with cooking spray, and then quickly stir the butter and marshmallows until combined.
Pour melted marshmallows over bowl of dry ingredients and stir quickly to combine, while the marshmallow mixture is still warm. Once combined, add about half of the reeses pieces to the mixture, then stir.
Pour/scoop mixture into prepared pan, and press into pan as needed. Immediately, sprinkle the remaining reeses pieces over top and gently press down just a bit if needed. Add a few pretzel pieces and a few broken chips on top, as desired, and gently press down to adhere.
Microwave caramel bits and heavy cream (or milk) in a small bowl for 30 seconds at a time (stirring as needed) until melted. Drizzle over pan of krispie treats (you may add caramel to a thick ziplock type bag to make a nice even drizzle, if you wish)
Set aside to cool (at least 15 minutes) before cutting. Enjoy!