Yes you can! Use a 6-inch round baking pan, well sprayed with baking spray. To ease removing the cake later, make a sling out of 2 long, skinny pieces of parchment paper, placing them perpendicularly to each other in the cake pan. Then, line the pan with a parchment paper collar before pouring in the brownie batter. This will help to keep the mousse from sticking to the pan when you top the brownie layer. A reader generously sent me her pictures using this method. Check out her cake decorations using hot fudge sauce instead of chocolate shavings. It's so pretty!