Prepare a 9x9 inch square cake pan with non-stick cooking spray and line with parchment paper; set aside
In a large stockpot, melt the butter and mini marshmallows over low heat until the marshmallows are melted
Stir in the vanilla extract and salt
Remove the pot from the heat and stir in the Rice Krispie cereal and mix until fully combined
Stir in the additional 2 cups of mini marshmallows to the Rice Krispie Treat mixture
Using a spatula or wood spoon, scoop the mixture into the prepared pan
Using a piece of parchment paper, press the mixture down into the pan into an even layer and allow the Rice Krispie Treats to cool for approximately 30 minutes
Remove the rice krispie treats from the pan and cut them into 16 squares, serve and enjoy! (If you are not serving right away, wrap the rice krispie treats in cellophane to keep soft and fresh)