Line a 15x10" baking pan with foil and grease lightly.
In a large saucepan over medium heat, melt marshmallows, butter, and peanut butter, stirring constantly until mixture is smooth. Remove from heat. Add cereal and stir until evenly coated.
Using a greased spatula or greased hands, press mixture evenly into greased, foil-lined pan. Spread frosting over cereal mixture to within 1 inch of edges, leaving the border empty.
Starting with the longest side and using the foil to help, roll up the dessert like a jelly-roll, carefully peeling away foil as you go.
Once finished, you should have a tight log with a spiral of frosting inside. Wrap the entire roll in greased foil or plastic wrap. Store in refrigerator, seam side down, for about 1 hour or until firm. Cut into 1/2-inch slices to serve. Make 30 slices. Enjoy!