Preheat the oven to 350 degrees . Grease a 9-by-13-inch baking dish. In a large pot, melt the butter over medium-low heat. Stir in 4 cups marshmallows until melted. Remove from the heat and stir in the cereal and 1/2 cup peanuts.
Transfer the mixture to the prepared baking dish and press into an even layer. Sprinkle the chocolate chips and the remaining marshmallows and 1/2 cup peanuts on top. Bake until the chocolate melts, about 5 minutes. Let cool for 30 minutes, then refrigerate until the chocolate is firm, about 2 hours. Cut into 1-inch squares.