Coat a muffin pan with cooking spray. Fill each cup halfway with your favorite brownie batter. Coat the bottom of a second muffin tray (the same size as the first) with cooking spray, then place it on top of the filled cups and press down until the cups almost touch. Bake at 350° for about 24 minutes. Let the top pan cool for 10 minutes before carefully removing it. Let the brownie bowls cool in the pan for 10 minutes more before carefully removing them.