Line a 9×13-inch baking pan with parchment paper. Lightly grease the parchment.

Melt the butter over medium heat in a very large pot. Once melted, add the marshmallows and stir until completely melted.

Remove from heat and stir in the vanilla extract and salt.

Fold in the cereal until each piece is coated with the marshmallow mixture.

Transfer the mixture to the prepared pan. Using a silicone spatula, gently spread the mixture to fit the pan.

Lightly grease the back of a flat spatula and very gently press the mixture down into the pan without packing it.

Allow the treats to set for at least 1 hour at room temperature.

Lift the rice krispie treats out of the pan using the edges of the parchment paper and cut into squares.

Store leftover treats at room temperature for up to 3 days in an airtight container.