The last couple of weeks I have taken more than a share of cake decorating classes, either using buttercream or fondant and along the way, I picked up a couple of tips and tricks that can help you make that plain cake into a picture perfect decorated cake. But out of all the tips and tricks that I have picked up one holds the top from all the rest, every single class, every single teacher can not stress enough about this being the most important of all steps.
Crumb coat the cake – ALWAYS!
A crumb coat a thin layer of frosting that keeps crumbs where they belong–on the cake–not the frosting! While this is the way to go if you are covering your cake with fondant, it’s also a good practice if you are covering the cake with buttercreams as well or any other kind of frosting. This easy step will make your final layer or frostings go on smoother and cleanly and will look more professional. In order to accomplish a good crumb coat follow these steps:
Let your cake COOL COMPLETELY on a cooling rack. If you place in the refrigerator overnight, even better – since this will “harden” the cake a bit, and since the cake is cold the buttercream will go on smoothly.
You’ll need your icing to be thinned out a little bit so that the crumb coat will be as thin as possible. To thin your icing, stir in a few drops of milk or water (I even read somewhere to use corn syrup) until the frosting is nearly the consistency of a glaze to just barely cover the cake in a very thin layer. Don’t worry about some crumbs getting in the frosting of the crumb coating; those crumbs will be sealed in when this layer dries.
Spread a THIN layer of frosting, you should still be able to see the cake itself through the frosting – some professionals also call this “dirty icing”. For easier smoothing, it may help to dip the spatula into hot water, wipe dry and glide it across the entire surface. Place the cake back in the refrigerator for 1-2 hours, which allows the cake to settle and the frosting will crust over and harden slightly, which is the secret for your next and final layer of frosting (or fondant) to go on smooth and perfect.
In two of my classes the teacher showed us to use paper towel, specifically the VIVA brand to smooth even further the top and side of the buttercream crumb coat - this obviously will not work if you have a ganache type frosting. Cover the cake with a strip of paper towel and gently, with the palm of your hands, using circular motion, smooth the cake around. NOTE: BEFORE you do this, make sure the crumb coat has sat for at least 20 minutes to form a crust. The best way to “test” if is ready for the paper towel part, is to touch it with your hands, if no frosting sticks, then you are ready to do move to this phase.
Obviously, there are tons and tons of resources on the internet for this, as well as videos. A good search will brig you even more tips and tricks for that perfect picture frosted cake.