Grease the baking pan with a thin layer of butter or line it with parchment paper to prevent sticking.
Place the butter and marshmallows into a large saucepan over medium heat. Use a rubber spatula to gently stir the mixture until the marshmallows are fully melted and the mixture is smooth, about 5-7 minutes. The mixture should be bubbly and fragrant when done.
Remove the saucepan from heat. Gradually add the rice cereal to the marshmallow mixture, folding gently with the spatula until evenly coated and no dry cereal remains. The mixture should be sticky and slightly glossy.
Transfer the mixture into the prepared baking pan. Use a spatula or wax paper to press the mixture evenly into the pan’s surface, creating a compact layer. Let it cool in the pan for at least 15 minutes or until set.
Once cooled, remove the treats from the pan by lifting the parchment paper or inverted pan. Decorate the top with red, white, and blue candies, pressing them gently into the surface to create a patriotic pattern.
Cut into squares or rectangles with a sharp knife. Serve immediately or store in an airtight container for up to 3 days.
