Prepare the Baking Dish: Line a 9x9-inch baking dish with parchment paper, leaving a little overhang on the sides for easy removal later. Set aside.
Melt the Butter: In a large saucepan or pot, melt the butter over medium-low heat until completely smooth.
Melt the Marshmallows: Add 4 cups of mini marshmallows to the melted butter. Stir continuously until the marshmallows are fully melted and the mixture is smooth and creamy.
Mix in the Cereal: Add the Rice Krispies and Golden Grahams cereals, plus ½ cup of mini marshmallows. Gently stir until everything is evenly coated in the marshmallow mixture.
Press Into the Pan: Transfer the mixture to the prepared baking dish. Using a lightly greased spatula or your hands, gently press it into an even layer without packing it down too firmly.
Add the S’mores Topping: Sprinkle the chocolate chips and remaining ½ cup of mini marshmallows evenly over the top. Gently press them into the surface so they stick to the bars.
Cool and serve: Let the treats cool completely before slicing into squares. Enjoy!