In large bowl, combine marshmallows and nuts. Set aside.
In medium saucepan, melt butter over medium low heat. When almost melted, stir in chocolate chips and continue stirring until melted and combined with butter. Remove from heat and immediately add to marshmallow nut mixture. Stir to combine.
Set aside to cool slightly.
Meanwhile, on a sheet of aluminum foil about a foot long, evenly sprinkle ¼ cup of powdered sugar down center of foil lengthwise. Drop half of chocolate marshmallow mixture along length of powdered sugar on foil Roll into a log (does not need to be perfectly round). Sprinkle ¼ cup of powdered sugar along chocolate marshmallow mixture. Seal up foil and roll into a more cylindrical log. I used a toilet paper tube to help me make it a bit more uniform.
Repeat with remaining powdered sugar and chocolate marshmallow mixture.
Place logs in freezer or refrigerator (either will work) until hardened.
To serve, unwrap log from foil and slice into pieces about ¼-inch thick. Serve immediately on a platter. (it's ok if they do not stay cool as they will maintain their shape but if it's warm where you are, you don't want them sitting out too long).
Notes
These are easy to make ahead! Instead of refrigerating, label and free them up to three months. When ready to serve, remove from freezer and allow to thaw slightly on kitchen counter, about 30 minutes. Follow recipe instructions for slicing and serving.