Follow the box mix directions and make a batch of brownies. Remove them from the oven when they are JUST shy of being perfect. Maybe a minute or two before necessary. You want the tops to be ever so slightly spongy.
Set them out to rest for about ten minutes so they are still warm but have settled.
Sprinkle with the chopped nuts, caramel chips and marshmallows.
Use a microwave or double boiler to melt the chocolate chips. When they are fully melted and liquidy, use a spoon to lightly drizzle the chocolate over the tops of the brownies.
Wait for the entire mix to cool and then cut into 1 inch squares.