Lightly grease the bottom of an 11x14 baking pan with cooking spray and line with parchment paper.
In a large pot over low heat, melt the butter and stir in the salt.
Set aside 1 ½ cups of mini marshmallows to mix in later. Then pour the remaining marshmallows into the pot with the butter and melt over low heat. (Stir constantly. Remove from heat as soon as melted.)
Once the marshmallows have melted, remove the pot from the heat and add the Rice Krispies cereal, the 1 ½ cups of mini marshmallows set aside earlier, 1 cup of Reese’s peanut butter cup minis cut in half, ½ cup peanut butter chips, and ½ cup semisweet chocolate chips. Gently fold together until evenly combined.
Pour the mixture into the baking pan and spread it out evenly.
Top with the remaining Reese’s peanut butter cups, peanut butter chips, and semisweet chocolate chips and gently press it into the bars to help them stick.
Allow your treats to cool in the pan for 30-45 minutes. Cut, serve, and enjoy!