Grease a 9×9-inch baking pan with cooking spray or butter.

In a medium saucepan, melt the unsalted butter over low heat.

Once the butter is melted, add the mini marshmallows, stirring continuously until fully melted and smooth.

Stir in the vanilla extract and salt until well combined.

Remove the saucepan from heat and immediately add the crispy rice cereal, mixing until all the cereal is coated with the marshmallow mixture.

Transfer the mixture into the prepared baking pan. Use a spatula or your hands (lightly greased) to press it down evenly.

Allow the mixture to cool in the pan for about 15 minutes.

Once cooled, cut into squares or rectangles, depending on your preference.

If desired, melt some chocolate and drizzle it over the bites, or sprinkle with your choice of toppings.