Line a 9x9-inch pan with aluminum foil. Spray foil with non-stick spray, set aside.

In a large pot, over medium-low heat, melt the butter. Once butter is melted add 6 cups mini marshmallows and salt (if using). Stir constantly until marshmallows are melted.

Remove from heat and stir in Rice Krispie cereal. Stir until just barely coated in marshmallow mixture. Now stir in the remaining 2 cups of mini marshmallows.

Pour mixture into prepared pan and press evenly into the pan.

Allow to cool completely before cutting into squares. Serve and enjoy!