Line a 13x9 pan with good parchment paper. Grease the parchment a little. Set that aside for a second.
Melt butter in a big pot over medium heat, then toss in marshmallows. Give them a good stir until they're entirely melted.
Off the heat, it goes! Quickly stir in some vanilla and a pinch of salt. Then, gently fold the cereal until every last bit is coated in this marshmallow mixture.
Transfer our gooey mixture into the prepared pan. Grab your rubber spatula (light greasing can keep sticky messes away) and spread the mixture evenly. Then, gently grease the spatula's back and press that mixture into the baking pan.
Let these treats rest at room temperature for 1 hour to 24 hours. Cover them tightly if you want them to sit out for more than 2 hours.
Use the parchment paper to lift the whole thing off your baking pan, then slice it into squares. Enjoy.