Smoothing a cake eludes most cake decorators. It is something you practice and practice. Everyone I know has tried at least six different methods for smoothing a cake. Some shops have specific methods and you learn them or else. The most famous cake smoothing technique I am familiar with comes from Sylvia Weinstock's shop. Her people can smooth a cake faster than anyone I've ever seen! 30 to 45 seconds a tier. Yep, 30 to 45 seconds.
I am not going to say this method will get you to that speed, but if you check the photos on my flickr page you can clock my process on this one. The times are actual and you can see how long it took me to do this, including taking photos of it.
1. Put a piece of non-skid padding on the turntable. Set your cake on top of it and you cake won't slide as you are smoothing it.
2. Start with a crumb coated cake. It should come straight out of the fridge and be well chilled. This makes the process a whole lot easier.
3. Ice cake, sides, top and somewhat smooth it as you apply. Not a lot, though and don't try to make it perfect as you apply the frosting on this pass. At the bakery, we always add more and then remove what we need to in order to get it ultra smooth.
4. Now for the magic! You will need one of these:
it is a painting edge sold at Ace Hardware. I cannot find this kind anywhere else! It is made out of aluminum and is very thin! That's what makes it work so well! I even bought one in Sugar City, Idaho once when I needed one. Thank goodness for old style hardware stores!
5. Holding it in your dominant hand, in a vertical position you are going to spin your turntable while you hold the painting tool close to the frosting. Keep it as vertical as possible as you want an even side surface. Put just a bit of pressure on it as you turn the cake. Now wipe off the excess frosting.
6. You will notice that certain parts of the cake have grooves where the icing isn't as thick as other parts. Illustrated in this picture; notice the bottom of the layer. Add more frosting to those areas. just glob a bit on in places where you feel it is needed and begin smoothing again.
7. This should take some practice. If you want to get good at this, you will need to practice this over and over again. Once you get it down though, it is like riding a bike. It was so much easier today than when I started doing it over a year ago.
8. Check that cake now! It is ready to have the top smoothed.
9. Wipe off your tool and remember to wipe it off every time you touch the cake at this point. You can drag the smoother toward you:
10. or away from you. Use the method that you find most comfortable. For the longest time I pulled the tool toward me. Then one day I decided to try it the other way and got amazing results. The key it to use the lightest touch you can possibly use. Barely touch the frosting at this point. When you begin, you may have to do this for 30 minutes or more to get it right.
You will also find that you drag the tool a bit deep in parts and you edges are wobbly. Keep in mind: unless it is a wedding cake you are going to add a border, so most likely it won't matter if it is wobbly. If you are doing a wedding cake, there usually isn't a top border so you need it to be even. Add a bit more frosting and begin again.
11. You now have a smoothed cake. Add some decoration to it.
12. Add the bottom border.
13. Add a top border and any other decos you wish.
Now go practice. This should take a bit of practice. I started at 1:18 and finished at 1:47. With photos that's 30 minutes start to finish. Once you've got it down, come point me to a few pics of your own! Feel free to ask questions in the comments too.