Line a 9"x9" baking pan with parchment paper.
Place 1/2 cup (1 stick) of unsalted butter in a large pot on the stovetop. Turn the oven burner on medium heat and allow the butter to fully melt.
Once the butter is completely melted, add in a 10oz bag of marshmallows, and stir the marshmallows within the melted butter over medium-low heat with a silicone baking spatula until the marshmallows are completely melted.
When the marshmallows are completely melted and evenly combined with the melted butter, add in 1 tbsp of vanilla extract, along with 1 tsp of salt, and stir until everything is evenly combined.
Turn the oven burner off. Set the pot on a thick towel on the kitchen counter so that it is no longer on the hot burner.
Finally, add in 6 cups of rice krispie cereal and fold the cereal into the marshmallow mixture until the rice krispie cereal is completely coated with the marshmallow mixture.
Now that everything is combined evenly pour the rice krispie treat mixture into a 9"x9" parchment paper lined baking pan.
Press down on the mixture with a piece of parchment paper. Trust me on this one! I have tried pressing down the rice krispie treat mixture with my spatula or with my hands, never again. Parchment paper is definitely the answer!
At this point you can add some fun sprinkles as a topping if you want!
Pop the rice krispie treat mixture into the refridgerator for 1-2 hours before cutting it up into delicious treats.
Once the rice krispie treat mixture is completely chilled you can pull the chilled mixture out of the 9"x9" pan by grabbing the sides of the parchment paper and placing the chilled mixture on a cutting board.
Now you can cut your rice krispie mixture into rice krispie treats and enjoy!