cake or brownies

Last night I forgot that I had promised to make a dessert for the Staff Appreciation Lunch today. So I hastily got the ingredients together to bake. I took two boxes of brownies, followed the directions but before baking added some vanilla and a sleeve of crushed Oreo cookies. Unfortunately I was so tired that I forgot to look at the pan sizes and saw that one box could have easily made a 9 x 13 pan of brownies and I threw the whole shebang into a pan that size. So they are either really thick brownies or a brownie cake. If they're a cake do I have to frost it? No frosting on hand so I would have to make one. I'm thinking maybe powdered sugar would be good enough to dress it up.