Mix the cake mix, butter, and egg until combined. Press mixture into a greased 9 x 13 pan. Bake at 350F for 20-25 minutes, until the edges are golden.
Sprinkle marshmallows over the baked crust and bake for an additional 5 minutes.
To make the topping, melt peanut butter chips, butter, and corn syrup in a saucepan over medium heat. Stir until smooth. Remove from heat and add cereal and peanuts. Once combined, spread mixture evenly over the base. Allow to cool completely before cutting into squares.
