Rocky road bars are the great for any impromptu get together! Pile them high on a plate for a night around the pool for a dessert kids and adults will both love.
Preheat oven to 350°F. Line a 9x13 pan with foil and spray with nonstick spray. Set aside.
In a large bowl, combine cake mix, melted butter, egg, water, and vanilla. Spread into prepared pan and bake for 20 minutes.
Immediately upon removing pan from oven, sprinkle evenly with mini marshmallows and place back in the oven for 5 minutes or until marshmallows are puffy but not toasted.
Sprinkle with chopped peanuts and set aside.
In a microwave safe bowl, heat chocolate chips and butter in the microwave, stirring every 15 seconds until smooth. Drizzle over bars.