A while back, someone posted a link to a product that was used to smooth buttercream. It was something that looked like a cake pan with no bottom. I hope I explain myself. The sides of the ring would be filled with buttercream, the cake placed inside, then the top would be frosted and you would smooth the top of the cake using the ring as a guide, then the ring would be heated with a hair dryer, and the ring would slide out, leaving a perfectly iced cake.
I hope someone out there can help me out.
Yes they're called cake rings... most bakery supplies should stock them. Or you can probably just google. They're great for building mousse cakes and such in as well. You can also bake in these if you place them on a parchment-lined sheet pan (a very FLAT one lol), and they're great for molding frozen mousses and stuff.
A tip: If you line the ring with acetate or parchment first, they're a lot easier to unmold--no heat gun or blow torch needed. Place the cake on top of something that is smaller than it (like salt canister or something) and slide the ring DOWN to unmold. Comes off a lot easier than trying to lift it up.
Check this out:
Try googling cake rings or cake forms
and one more thing (I know they keep popping in my head lol): When you build your cake in a ring you'll likely need to trim it. If you bake an 8" cake and want to build it in an 8" ring, you'll line the ring with buttercream, which will obviously leave you with less than 8" for cake, so you'll need to "shave" the outside of your cake off to fit it inside the buttercream wall.