Here’s an easy way to make a box of brownie mix look, well… fancy.
First, make a pan of brownies. Before you put them in the oven, mix 1/4 cup of creamy peanut butter with 1/4 cup powdered sugar in a small bowl. Slowly stir in milk, 1 teaspoon at a time, till you can stir it easily and its about the consistency of soft frosting. Spoon it all into the corner of a ziplock bag, and snip a tiny bit of the bag corner off. (Test the line size by squeezing a short line of peanut butter out. Its really easy to snip more off to make the hole larger, and really annoying to transfer it into another ziplock because you made the hole too large.)
Then start at one end of the pan, and make a nice line of loopty loops along one edge. (If you’re less confident in your loopty-loop skills, just write out “eeeeeeeeeee” in cursive). Rotate the pan 180 degrees and do it again. And again, and again. Then put it in the oven and bake like normal.
* * * UPDATE * * *
OK Stacy, since you asked, and I didn’t have an after photo to show, I baked up a pan tonight. (Hubbs didn’t even mind.) Here’s what they look like “after.” – you can see peanut butter doesn’t melt down like you might expect, but really stays in place. In the bottom row of loopty-loops I did a double layer of peanut butter, and you can see how the two lines are still totally distinguishable even after baking.
This would be a great way to write “happy birthday,” or draw any other sort of decoration you might want.