The way I did it, I baked all my layers on Wednesday and planned to do all my covering on Thursday. Friday we would check into the hotel and have our rehearsal dinner, and Saturday was wedding day. So when I woke up on Thursday morning, I had about ten cakes waiting for me. It was actually intimidating when I peeled the foil off of them and put them all on one countertop to look at. They were taunting me. "Can you do this?" they asked. "Yes?" was my answer.
Especially because not all my cakes were beautiful. So let me talk about four-inch cakes for a second. Four-inch cakes, it turns out, are special beasts. I ended up baking twice the amount of four-inch cakes I needed (I needed just one of each flavor, baked two of each flavor), because each time, they cake out kind of weird. I had a cake whose entire outer edge fell off. I had a cake that had a giant crater in the bottom. I had a cake that looked like a parallelogram. And I had a cake with a top you could skid own. I baked twice as much, because I figured that between the four cakes, I would be able to put together four sort-of complete layers, and keep it all held together by covering it in frosting.
The first step in covering, after getting over the intimidation of 10 cakes staring you in the face, baiting you, is to slice them in half lengthwise to make layers that are about one-inch tall (maybe a little less -- just try to make them equal, whatever height that ends up being). Some people use a cake leveler for this, but I'm old school (and don't have the storage for gadgets), so I use a knife. And I don't say that lightly: because this is where I started sweating, and I didn't stop for about 5 hours (it was gross). The key, I've found, it to have a ruler handy, and to keep your knife as flat as possible. As well, don't be afraid for this or the frosting, to contort your body to get your eyes level with the cake and make sure you are being as horizontal as possible. And lastly: little by little. First, just notch the cake sides a little bit, only cutting a small slash less than half an inch deep all the way around. Then, just connect the dots, and slowly cut deeper and deeper, never going all the way across, but just spinning the cake 'round and 'round, going deeper and deeper.
Oh, and practice. You won't get it right the first time, most likely.
After you're done leveling your cakes, you'll be left with a giant bowl of cake scraps. Some people say you should use these for cake pops. I 1) find that a waste, and with that 2) find cake pops disgusting, so I like to call this the Baker's Bonus, and prefer to use the cake scraps to stress snack on while I make the rest of the cake. And for dinner that night. And for breakfast the next day. I just really like, cake, okay?
So, step 1 is the leveling (or "torting," if you're fancy). Step 2 is the frosting. I think I may have said this in the frosting post, too, but always make more than you need. I made three gallon-sized bags of Italian meringue buttercream and it was only just enough to fill the cakes. I wish I had made a third batch of buttercream, just because having that extra safety of extra buttercream makes it a lot easier, and a lot less stressful, when frosting the cakes.
The stacking and filling process is fairly straightforward. Put a glob of frosting on the cake, spread it out evenly, and throw the next layer on top. The key to doing a good job is really about knowing the right amount to put on. Let's get real: we all love frosting. And more is always better than less, right? Wrong. I made cakes of four tiers, meaning three layers of frosting, plus frosting all around the cakes, plus a sweet fondant covering the frosting. Exercise caution in how much frosting you put inside and around the cakes. You want to highlight the cake with the frosting, not suffocate it.
As well, frosting is not solid, whereas cake is solid. The more frosting you have, the more delicate your cake becomes, and the more susceptible it becomes to tilting, leaning, and altogether chaos. So keep the layers thin.
And I say "layers" as plural because around the outside of the cake there are 2 layers. The first is what's called a "crumb coat," and it locks in crumbs to keep your final cake smooth and beautiful, which is really important if you're not covering it in fondant. The crumb coat layer is so thin you'll be able to see cake underneath it. You refrigerate that coat to make it a smooth solid surface to put the final coat on, making it ready for fondant.
Once the cakes were covered, once I had four neat and tidy tiers, you would think I would be able to calm down. One step left. Step 3: fondant.
I don't have any pictures of me covering the cakes in fondant, just this shot of my prep station. You know why? Because it was so stressful that I forgot I even owned a camera. I was so focused on these cakes that I forgot I even had a name. Despite my practice and my best preparations (i.e. watching Yolanda Gampp's How to Cake It "Hacking Fondant" video about 87,000 times), working with fondant is not easy if you're not used to it. And I was not used to it. I got so nervous that it would wrinkle, it would crack, it would tear, it would stick, that my shirt instantly became drenched in my own stressed sweat, and I became an unintelligible fool.
So, my first piece of advice is: relax. It's just cake.
My pieces of advice of advice: 1) use more fondant than you need (but not too much more), 2) roll out to 1/8" thick if you can, 3) roll out on top of a non-stick mat and/or cornstarch, and 4) remember that it will taste good no matter what. Always remember: it will taste good no matter what.