You can press any of the mix-ins we've mentioned—from Fritos to bits of candied orange—on top of the brownies or cookies before they go into the oven for a "ta-da!" presentation. This is also a good place to put more fragile additions—such as popcorn—that would probably disintegrate if you stirred them into the batter. Another easy topping trick is to pull brownies out of the oven a minute or two before you think they're done cooking and dot the surface with mini marshmallows; then return the pan to the oven. It won't take more than two minutes for them to melt enough that you can spread them with a spatula. Let cool before serving or storing.