Prepare a 9×13 inch baking dish by lining it with parchment paper, leaving some overhang on the sides. Lightly spray with non-stick spray.
In a large pot or saucepan, melt the butter over medium-low heat for 2-3 minutes. Watch carefully and don’t let it brown.
Add the entire bag of mini marshmallows and stir constantly until completely melted and smooth, about 3-4 minutes. Mixture should look glossy with no lumps.
Remove from heat immediately. Stir in creamy peanut butter, vanilla extract, and salt until well combined and smooth. Work quickly as mixture will start to set.
Pour Rice Krispies cereal into the pot. Gently fold the cereal into the marshmallow mixture until evenly coated. Don’t overmix.
Quickly transfer mixture to prepared baking dish. Using a lightly greased spatula or hands, gently press into an even layer about 1 inch thick. Do not press too hard or treats will be dense.
Let treats cool completely at room temperature for at least one hour before cutting. Do not refrigerate.
Use parchment overhangs to lift treats from dish. Cut into 12 squares using a sharp knife, wiping blade between cuts for clean edges.
Notes
Use fresh marshmallows for best texture. Stale marshmallows result in hard treats.
Do not overcook marshmallows or leave on heat after melting. This causes hard treats.
Press gently into pan to maintain light, chewy texture. Pressing too hard makes them dense.
Store at room temperature only in airtight container. Refrigeration makes them hard.
For extra indulgence, add 1/2 cup chocolate chips or peanut butter chips with the cereal.
Standard marshmallow bags are 10 oz. If using a larger bag, measure out 4 cups of marshmallows.