Inspired by Oh Happy Day's "Mini Cake DIY," my big Sophia and I decided to make our own version. An obvious complication arose: neither of us bake. But, that's all part of the fun - for the 1-2 hours of getting baking supplies ready, prepping, and the actual baking, we got to talk a lot (moral of the story: bake with a friend). The house was filled with the scent of freshly baked goods, and afterwards, we served our experiment to the girls in the fireplace room. Oh, the joy of a three-day weekend!
We used Betty Crocker's brownie mix and simply followed the directions. A note for advanced bakers (and a note for ourselves), use a thinner tray so the brownie mix is stacked higher. That way, you can create a higher stack and more layers of frosting for later on. See Oh Happy Day's example.
We created our own frosting because in the house, there was only one type: milk chocolate. Brown frosting on brownies wouldn't exactly be aesthetic in terms of presentation. So with powdered sugar, pure vanilla extract, softened butter, and milk, we were able to make our own frosting (which tasted heavenly - especially if you have a sweet tooth).