Line a 9×13-inch baking pan with parchment paper. Lightly grease the parchment. I always use a very light mist of nonstick spray. Set aside.

Melt the butter over medium heat in a very large pot. Once melted, add the marshmallows. Stir the mixture until the marshmallows are completely melted.

Remove from heat, then immediately stir in the vanilla extract and salt. Finally, fold in the cereal. Make sure each piece of cereal is coated with the marshmallow mixture.

Transfer mixture to prepared pan. Using a silicone spatula (greasing it lightly helps), gently spread mixture to fit the pan. Lightly grease the back of a flat spatula and very gently press the mixture down into the pan. Do not pack it down with force, just lightly press down until it is secure in the pan.

Allow treats to set for at least 1 hour at room temperature, and up to 1 day. Cover tightly if leaving out for more than a few hours.

Lift the rice krispie treats as a whole out of the pan using the edges of the parchment paper. Cut into squares.

Cover and store leftover treats at room temperature for up to 3 days. To store, place in an airtight container, with sheets of parchment or wax paper between layers.