As you may recall, yesterday's post ended with torting the cakes (making 2 layers into 4). This is a good time to blow the dust off your cake turntable, if you have one. A turntable is an essential tool for decorating, but comes in handy for many other things, such as filling the layers. When you're shopping for a turntable, spring for the heavy metal variety; they spin smoothly and steadily and they tend to have a cool, vintage look. I'm hard-pressed to think of a single positive thing to say about plastic turntables.
You'll want to keep things in place when you're working with a turntable. If it came with a rubbery non-slip mat, lay that down first (you can cut one out of that shelf-liner material; it's the same substance). On top of that, place one of your foil-covered cake circles, and deposit a healthy smear of frosting to anchor the first layer of cake you lay down (either with your bare hands or with a cake lifter):
Using either a large offset spatula or a pastry bag fitted with a cake icer tip and loaded with about half a can of frosting per layer, start spreading out the frosting as evenly as possible. Cakes that have been refrigerated for a half hour beforehand may be easier to work with and less "crumby." Rotating the cake on the turntable while you lay down the frosting should help you immeasurably in your quest for an even cake.
Remove the two parchment circles as you go, but make sure one of them is on the "top cake"; your surface for frosting the whole cake will be that much smoother and relatively crumb-free.
Do all you can to keep the layers nice and even; get down to eye level with your cake and give it a spin on the turntable. If it wobbles like an old warped 33, you can probably shim up the layers by sneaking in some extra icing with your offset spatula before you frost the sides (another time when being able to rotate the cake on the turntable makes an even coat of frosting so much more attainable).
I have yet to be able to frost a cake perfectly smooth with the spatula, but after leaving the cake in the fridge for 15 minutes or more, I tear off a piece of parchment paper a little larger than my hand and "massage" any uneven spots until they're smooth.
I'm learning to not have a nervous collapse if the frosting on the cake isn't Royal Wedding-worthy. 99% of the time I've been able to hide minor imperfections under fondant, drop strings, writing, etc. Stay tuned for a final upcoming installation on the subject of pushing the limits of cakes made from box mixes!