Lightly grease a 9x9-inch pan with nonstick spray or line it with parchment paper for easy release. Set aside.

Melt butter in a large pot over low heat, stirring occasionally.

Add 5 ½ cups of mini marshmallows to the melted butter. Stir constantly until the marshmallows are fully melted and smooth.

Remove the pot from the heat and stir in the peanut butter, vanilla, and kosher salt until everything is evenly combined.

Gradually fold in the crisped rice cereal, mixing gently to coat all the cereal evenly.

Add the remaining 1 cup of mini marshmallows to the mixture and fold them in gently so they stay whole.

Transfer the mixture to the prepared 9x9-inch pan. Press it into an even layer using a greased spatula or lightly buttered hands. Do not press too hard to avoid making the treats too dense.

Allow the treats to cool at room temperature for 1-2 hours, or place the pan in the refrigerator for 30-40 minutes to set more quickly. Once firm, slice into 12 squares or your preferred size. Enjoy!