Prep a 9x13 baking pan with parchment paper so that the edges hang over the sides of the pan, and then spray with nonstick spray. Set aside.
Pour Rice Krispies into a large bowl and set aside.
6 cups Rice Krispies cereal
In a medium saucepan, melt butter over low heat. Add 4 cups mini marshmallows and heat, stirring frequently, until melted and mostly combined - it's okay that it's not fully incorporated, it's better that way!
6 tablespoons unsalted butter, 6 cups mini marshmallows
Turn off heat, add peanut butter and stir to combine. If the peanut butter you're using doesn't have added salt, you can add a pinch of salt at this point and stir to combine.
1 cup creamy peanut butter, Pinch salt
Immediately pour peanut butter mixture into the bowl of Rice Krispies, add Fluff and remaining 2 cups mini marshmallows and stir to coat and combine.
7.5 ounce container of Marshmallow Fluff
Turn out into prepared baking dish and press down into an even layer.Tip: If you have another 9x13 pan, you can use the bottom of that pan to press into the top of your dish for an easy way to get it evenly distributed! You can also spray your hands with a little nonstick spray and use your palms to press it down, or place another piece of parchment paper on top before using your hands to press it down.
Let set for at least 15 minutes, and then slice into 12 large bars. Serve and enjoy!
Video
Notes
You can store them at room temperature between layers of parchment paper in an airtight container for 2 days.You can also store them in the freezer for up to 1 month - again, in an airtight, freezer-safe container between layers of parchment paper.To defrost, just let them sit on the counter at room temperature for about 30 minutes before serving.