Line a 9-inch square baking dish with parchment paper.

Prep your ingredients so they're portioned out and ready to go once the recipe begins. Set aside 1 cup of the mini marshmallows.

Add butter to a large pot set on the stove over low-medium heat. Once it melts, add all of the marshmallows (except for the 1 cup set aside). Stir as they expand and lose their shape. Continue until the marshmallows are just melted.

Remove the pot from the heat, then stir in the vanilla extract and salt.

Working in a few batches, add the cereal and reserved 1 cup of marshmallows and stir until evenly combined.

Turn out cereal treat mixture into the lined pan. Using slightly wet hands, a greased spatula, or the slick side of a butter wrapper, lightly press the mixture into an even layer. Try not to use a lot of force to press it in and condense it as this can make the bars dense.

Let the bars cool down and set before lifting out of the pan and slicing into treats (this will take about 1 hour). These treats are best served fresh the same day or the next day, but will stay for several days in an air-tight container at room temperature.