I made a pan of these simple-but-lots Brownies for a Crowd last Friday for the Apprentice's choir coffeehouse night. (I left out the nuts and stirred in half a cup of rolled oats instead.)
At home I don't usually even ice brownies, or I might sprinkle them with chocolate chips before baking; but I wanted these to be more dressed-for-the-party. So after I let them cool a bit, I covered them with this topping:
1 bag semisweet chocolate chips
small amount of milk or cream--just a spoonful is fine
1/2 bag of mini marshmallows (or more)
Heat milk and chocolate chips together until chocolate is melted. Stir in marshmallows, but don't let them melt too much. Pour over brownies and let set (you might have to chill them to get it to set). This topping stayed just a bit gooey, but I think that was okay. Makes enough to cover a 10 or 11 by 15 inch jellyroll pan of brownies.