Line a large baking sheet** with wax paper and spray liberally with nonstick cooking spray. Pour cereal into a large bowl.

In a medium saucepan, melt the butter, salt, and 6 cups of the marshmallows together over low heat until marshmallows are almost melted–it should still be a little lumpy. Remove from the heat and immediately pour on top of the cereal. Stir until everything is coated, then add in the marshmallow creme along with the 2 remaining cups of marshmallows. Continue to stir until evenly mixed. Dump cereal mixture out onto prepared pan, and use a silicone spatula or wet hands to press the mixture into an even thin layer.

In a small saucepan heat the caramels and cream over medium heat until smooth and melted. Drizzle caramel evenly over the cereal mixture. Refrigerate until caramel is set and dry to the touch.

Melt half of the white chocolate (18 ounces) in the microwave until smooth and pourable. Drizzle white chocolate over the caramel cereal mixture, then use a knife or offset spatula to spread the chocolate evenly over everything. Refrigerate until chocolate has set.

Heat the remaining white chocolate in the microwave until smooth. Turn the sheet of rice krispies over onto its chocolate side (which is now set), then drizzle the melted chocolate over the rice krispies, using an offset spatula to spread the chocolate evenly. Immediately top with M&Ms and sprinkles. Refrigerate until chocolate has set, then use a knife to cut bark into several pieces.