For simplicity's sake, I decided to show you a design using only one color, but it works great for multi-colored designs, as well. Hubby loves Legend of Zelda, so this was the perfect design to put on a cake.
You will need parchment paper, piping gel, and decorator tips, as well as your icing. If you are new to cake decorating and these things sound foreign to you, scroll to the end of the post for some links to get you started.
Start with an iced cake. Make sure you used decorator icing, not the canned stuff. To create a smooth surface for decorating, smooth the icing as much as possible with an angled spatula, then let sit for 10-15 minutes to allow the icing to crust.
Cut a piece of parchment paper large enough to cover the cake.
Lay the parchment paper over the cake. Run your hands gently over the paper.
The warmth of your hands will warm the icing just enough to smooth out many of the little lines or dimples in the icing. The result will not be quite as smooth as fondant, but it will still be pretty smooth, and taste much better than fondant, too. :)
After smoothing for a few minutes, gently peel the parchment paper off the cake.
Again, this only works with decorator icing. If you try this with canned icing, you'll end up with a mess!
Look how smooth this cake is now!
Okay, now on to the fun stuff! You will need parchment paper, a print out of the design you want on your cake, some piping gel, and some cornstarch.
Lay a piece of the parchment paper on top of the design.
Using the piping gel, trace the outlines of your design. Don't worry if it's not perfect.
Continue until you have outlined your entire design.
Slide the design out from under the parchment paper, and you will be left with your design outlined on the parchment paper in piping gel.
Pick up the parchment paper and turn over, piping-gel-side down, on top of the cake. Make sure that you have placed it exactly where you want it, because once the paper is placed, you won't be able to move it.
Gently rub your hand over the paper, and then peel the paper off the cake.
Pretty cool, huh? You now have a perfect outline to follow as your draw your design.
Now you are going to need to fill a decorator bag with decorator icing in the color of your design. Use a small round tip on the bag; I used a size 4.
Trace over the piping gel with the icing. Take your time; this will be the outline that will show. It's not difficult, but it can be a little time-consuming. It's okay, the end result is worth it!
Continue until you have traced the whole design.
Next, you are going to use a tight zigzag motion to fill in the outline.
Continue until the entire design is filled in.
You're almost done! It looks pretty cool at this point, but we're going to finish it off a little.
Let the icing crust for 10 minutes or so. Meanwhile, put some cornstarch in a dish.
Dip the tip of your finger in the cornstarch, shaking off the excess. Use your cornstarched finger to rub out the zigzag lines from your design. Reapply cornstarch as necessary to keep your finger from sticking to the icing.
When you have smoothed out your entire design, you are officially finished with that part of your cake! Now just add a border or whatever else you want, and then show off your cake with your perfect design!
As promised, here are some links to get you started building up your cake decorating supplies:
This is a great beginner's set of cake decorating tools:
For a little more money, you can get the decorating caddy complete with all of the tools you need for Wilton Course 1. This is the set I personally have, although I have added a few individual items to my collection. But I love it!
I highly recommend the Wilton cake decorating classes, which are offered at many local craft stores. Click here to find classes in your area.