Start by greasing a 9x13-inch baking dish with a little butter or non-stick spray to prevent the treats from sticking.
In a large saucepan over low heat, melt 3 tablespoons of unsalted butter. Once melted, add 10.5 ounces of miniature marshmallows and stir continuously until completely melted and smooth.
Remove the saucepan from heat and stir in 1 cup of creamy peanut butter until fully incorporated with the marshmallow mixture.
In a large mixing bowl, combine 4 cups of Rice Krispies cereal and 2 cups of crushed pretzel pieces. Pour the marshmallow-peanut butter mixture over the cereal and pretzels, and stir until everything is evenly coated.
Now, fold in ½ cup of peanut butter chips and 2 cups of semisweet chocolate chips into the mixture. Make sure they are evenly distributed throughout.
Transfer the mixture to the prepared baking dish. Using a spatula, press it down firmly and evenly into the dish.
Allow the mixture to cool at room temperature for at least 30 minutes. For quicker results, you can place it in the refrigerator to set more quickly.
Once set, cut into squares or rectangles. Serve immediately or store for later enjoyment!
