Line a 9x13 pan with foil. Grease well using butter for best results.
In a large microwave safe bowl (or a saucepan for the stove), melt butter. Add marshmallows to bowl, heat at 45 second intervals, stirring in between until melted and smooth.
Meanwhile, mix together cereals in a large bowl.
Add caramel sauce and ¼ teaspoon of salt to melted marshmallows. The caramel sauce will sink straight to the bottom so stir well to combine. Pour over cereal and mix well. Add in halved Rolo candies and stir again.
Transfer this mixture to prepared pan. Take a turner spatula and butter the back of the flat side well. Use it to press the bars firmly into the pan. Take a salt shaker and lightly salt the top of the bars. Set aside to cool and set up before cutting into bars.
Recipe by Crumbs and Chaos at http://www.crumbsandchaos.dreamhosters.com/2013/04/double-chocolate-salted-caramel-rice-krispie-treats/