Prepare your pan by lining a 9×9 inch baking dish with parchment paper, leaving some overhang for easy removal later. Lightly coat the parchment with cooking spray.
Melt the butter in a large pot over medium-low heat. Watch it carefully so it doesn’t brown—you want it just melted completely.
Add the marshmallows to the melted butter and stir continuously until they’re completely melted and smooth. This should take about 3-4 minutes. Reduce heat if they start to brown at all.
Remove from heat and add peanut butter, stirring vigorously until fully incorporated and smooth. The mixture should be glossy and uniform.
Mix in the salt and vanilla extract, stirring until well combined. These additions enhance the flavor profile significantly.
Fold in the crispy rice cereal one cup at a time, gently folding with a wooden spoon until all cereal is evenly coated. Be careful not to crush the cereal—you want to maintain that signature crunch!
Transfer the mixture to your prepared pan and press it down evenly using a piece of parchment paper or a spatula lightly coated with cooking spray. Don’t compact it too hard or your treats will become dense.
Sprinkle with mini chocolate chips if using, gently pressing them into the surface while the mixture is still warm so they adhere.
Allow to cool completely at room temperature for about 30 minutes before cutting into squares.