Start by greasing your square pan with nonstick cooking spray. This step ensures the treats won’t stick when you try to cut and serve them later.
Set a large pot over medium heat and melt your butter. Once melted, toss in the mini marshmallows and stir constantly until they’re fully melted and smooth. It only takes a few minutes, so keep an eye on it.
Remove the pot from the heat and stir in vanilla extract and a pinch of sea salt. Then, whisk in the creamy peanut butter. The peanut butter will blend beautifully with the melted marshmallows, creating a rich and flavorful base.
Add the crispy rice cereal to the pot and gently fold it into the peanut butter mixture until evenly coated. For an extra gooey texture, stir in one cup of mini marshmallows at this stage.
Pour the mixture into your prepared pan, then lightly press it down with a greased spatula or your hands. Be careful not to pack it too tightly, as pressing too hard can make the treats overly dense. Sprinkle flaky sea salt on top for a final touch.
Allow the treats to cool for about an hour. Once they’ve set, cut them into squares and enjoy!