Line a 9-inch square baking pan with parchment paper, leaving enough parchment overhang to lift the bars out of the pan. 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 and salt (if using). Stir the mixture until the marshmallows are completely melted. Remove from heat, and then fold in the cereal. Make sure each piece of cereal is coated with the marshmallow mixture.

Transfer mixture to prepared 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 and even in the pan.

Allow treats to set for at least 2 hours at room temperature, and up to 1 day. Cover tightly if leaving out for more than a few hours.

Lift the cereal treats out of the pan using the edges of the parchment paper. Cut into squares. Line a large baking sheet with parchment paper or a silicone baking mat. Set aside.

Melt the white chocolate in a double boiler on the stove, or simply use the microwave: Place chopped white chocolate in a large microwave-safe bowl, and microwave in 20-second increments, stirring after every 20 seconds until completely smooth. Hold the treat and dip the bottom into white chocolate, making sure to coat it generously. Place treats, white chocolate side up, on prepared baking sheet. Allow chocolate to set at room temperature for about 1 hour, or in the refrigerator for 20 minutes.

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.